05 Nephrology

SECTION 5

Nephrology 29.

An Approach to a Person with Proteinuria or Microalbuminuria Ravikeerthy M

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30.

Early Identification of the Diabetic Nephropathy; Beyond Creatinine Vivek Pal Singh, S Avinash

156

31.

Approach to Hematuria PP Varma, T Mohanty

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An Approach to a Person with Proteinuria or Microalbuminuria

C H A P T E R

29

Ravikeerthy M

“The ghosts of dead patients that haunt us do not ask why did not employ the latest fad of clinical investigation. They ask us, why did not test my urine�

Sir Robert Hutchison Kidney plays an important role in maintaining body homeostasis by changing the composition of urine to maintain electrolytes and acid-base levels and also got endocrine function which maintains metabolism.1 Glomerular filtration rate (GFR) is normally used to assess the kidney function which may not be useful in many clinical settings. Abnormalities kidney function can not only be the early sign of kidney disease but can also reflect many systemic conditions.

Normally plasma proteins crosses glomerular capillaries and mesangium without entering urinary space except a small portion of small density proteins which are excreted into the tubules and are reabsorbed by the proximal renal tubule.2 Proteinuria which may be a incidental finding in many patients can be the early sign of a serious kidney and systemic disorder. Several studies have revealed that proteinuria is associated with increased mortality.3 Therefore early detection and treatment can prevent morbidity and mortality.

History of proteinuria dates back to 2000 BC in Hindu literature. Hippocrates has described proteinuria as foamy urine. A normal person excretes 150-200mg of protein in urine as result of tubular secretion which

Table 1: False positive

False Negetive

Concentrated urine

Diluted urine

PH>7

pH<4

Presence of gross Protein < 300mg/day hematuria/WBC/mucous/ semen/vaginal discharge

includes lessthan 30 mg of albumin.2,4 This amount of urinary proteins can be detcted by the dipstick testing.3 Proteinuria can be transient following heavy exercise. Persistent proteinuria needs to be investigated. False positive and false negetive results are possible in a dipstick test (Table 1). Conditions are as follows: Proteinuria is classified into microalbuminuria and macroalbuminuria.5 Microalbuminuria refers to a subclinical condition with increased urinary albumin excretion. By definition microalbuminuria is the excretion of albumin in urine at rate of 20-200 mcg/min (30-300 mg/day) or albumin to creatinine ratio of 2.5 to 25 mg/mmol in males and 3.535mg/mmol in females.National health and nutritional examination survey (NHANES)study revealed that the prevalence of microalbuminuria in age group of 6-80 years is 6.1% in male and 9.7% in females. Prevalence progressively increases with age.6,7 Prevalence in hypertension around 4-16%.8 Most of them progress to overt proteinuria and end stage renal disease over a period of time. Microalbuminuria is an early maker of nephropathy or ESRD in Diabetes and Hypertension and studies have shown that it is an independent risk factor for atherosclerotic cardiovascular disease.3,4 Studies have also shown association of microalbuminuria and increased risk of cardiocascular disease in obese nondiabetic individuals.9 Studies like PREVEND (Prevention of renal and vascular end stage diseases), HUNT(nord-trondelag health study) and EPIC (Europian prospective study) have shown that in persons with microalbuminuria but are nonhypertensive and nondiabetics have increased risk of cardiovascular disease by 40% and 29-50% risk of cardiovascular mortality including stroke.5 Glomerular endothelial dysfunction may be cause for microalbuminuria which explains the association with atherosclerosis.10 Microalbuminuria is also associated with increased risk of stroke.5,11

Urease producing bacteria Positively charged by rising pH proteins like immunoglobulin light chains and beta2 microglobulins

There are various risk factor for development of proteinuria or microalbuminuria. They are as follows 1.

Male sex

2.

Advanced age

Iodinated contrast agent

3.

High body mass index

Contamination with disinfectant like chlorhexidine

4.

Smoking

5.

Diabetes mellitus

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6.

Hypertension including elevated systolic blood pressure.

Proteinuria is classified as follows 1.

Glomerular- Primary and secondary

2. Tubular 3. Tubulointestitial 4.

Overflow

NEPHROLOGY

Causes of proteinuria are A.

Benign:

1.

Excercise

2.

Dehydration

3.

Stress

4.

Infections

5.

Orthostatic

6. Pregnancy 7.

Heat Injury

B. Organic causes includes various glomerular diseases like Glomerulonephropathies (including IgA nephropathy), diabetes mellitus, hypertension, collagen vascular diseases, malignancy, infections like HIV, hepatitis B etc and drugs and poisoning. tubular diseases like uric acid nephropathy, Fanconiâ&#x20AC;&#x2122;s anemia, heavy metal poisoning and drugs like NSAIDs. Overflow proteinuria conditions are hemoglobinuria, myoglobinuria, multiple myeloma and amyloidosis.3

APPROACH TO DIAGNOSIS

As in any other situation care history and physical examination are mandatory in making the diagnosis and further evaluation. A detailed history can give clue to the use of drugs like NSAIDs and illicit drug abuse and also systemic diseases. Careful examination needs to be carried out to find out the other end organ damages as in diabetes and atherosclerosis. Physical examination may also be useful in collagen vascular diseases and other sytemic diseases. Strict glycemic control and blood pressure control can prevent or retard the progression of microalbuminuria to overt proteinuria eventually ESRD and other complications.3,4 Urine analysis should be repeated to exclude transient proteinuria.Once the persistant microaluminuria is established, it needs to be quantified.12 Quantification can be done using 24 hour urinary protein or timed overnight urine collection. Other methods used for albumin excretion are random urine sampling and spot morning urine sample (first void).5 Techniques of quantification are as follows.2 1.

Radioimmuno assay by double antibody technique

2.

Immunoturbometric method

3.

Laser nephrometer

4.

ELISA

5.

HPCL method

Blood sugar levels, creatinine, electrolye levels, protein creatinine ratio or albumin creatinine ratio and lipid profile needs evaluation in both type 1 and type 2 diabetes and hypertension. ECG, echocardiography and peripheral arterial doppler studies has to be done to assess the cardiac function as well as to assess atherosclerotic vascular disease. Serological studies to exclude HIV, hepatitis and collagen vascular diseases are to be carried out. urine analysis may reveal red or wbc cast and esinophils in tubulointestitial nephritis. Electrophoresis may be considered in multiple myeloma and hemoglobinipathies.

TREATMENT

Treatment of microalbuminuria and the condition that has lead to microalbuminuria is atmost important in order to prevent progression to end stage renal disease and also improve cardiovascular morbidity and mortality. Several studies have proven this fact that use of antiproteinuric agents totreat microalbuminuria retards progression to ESRD and better clinical outcome.

Angiotensin convertingenzyme inhibitors (ACEI) and angiotensin receptor blocker (ARB) are drugs of choice for the treatment of proteinuria or microalbuminuria.

ACEI are preferred over ARBs. These agents reduces intraglomerular pressure and preserves integrity of glomerular membrane which inturn reduces proteinuria.

ACEI and ARBs not only controls proteinuria but also controls hypertension. Several studies have shown that good blood pressure control retads the progerssion to ESRD. Dihydropyridine calcium channel blokers should better be avoided. Nondihydropyridine calcium channel blockers and beta blockers are also shown to retard the progression to renal failure. Statins have also shown the beneficial effects in teratment of microalbuminuria as they reduce protein traffic across proximal renal tubular cells. Good glycemic control in all diabetic patients also delays the progression to renal failure.

Apart from antiproteinuric therapy, life style modifications to reduce weight, regular exercise, salt restriction, dietary protein restriction are also required. Smoking cessation, avoiding unnecessary use of NSAIDs and other nephrotoxic drugs helps in preventing progression to renal failure. In patients with heavy proteinuria, severe exertion is to be avoided and supine or recumbent posture is encouraged.3,4,8

CONCLUSION

Proteinuria or microalbuminria is one of earliest and powerful sign of kidney disease and a marker of atherosclerotic cardiovascular disease. Treatment of microalbuminuria and the primary condition which has lead to proteinuria not only retards the progression to renal failure but also reduces morbidity and mortality.

Microalbuminuria can be seen commonly in general population, hypertension and diabeic patients. Hence careful investigation in persons with proteinuria in urine analysis and high risk patients can help prevent morbidity and mortality to great extent.

REFERENCES

Joseph V Bonventre:Adaptation of injury:Chapter333e:Harrison’s principles medicine:19th edition:1799.

kidney to of internal

2.

Ajay K Israni and Bertram L. Kasske:Laboratory assessment of kidney disease:glomerular filtration rate, urine analysis and proteinuria: Brenner and rector’s The Kideny :volume 1chapter 25: edition 9: 868-896.

3.

Fatemeh Akbarian, Hatim Al Lawati and Mohammed Ali Shafiee:Approach proteinuria in adults and elderly. Journal of Current Clinical Care 2011; 45-56.

4.

KK Venkat: proteinuria and microalbuminuria in adults:significance, evaluation and treatment. Southern Medical Journal 2004; 97:969-980.

5.

Adel E.Birbari, Nala Daouk and Ahmed Fawaz:Increased urinary albumin excretion:definition, prevalence,clinical significance and therapeutic implications. Lab Med Journal 2006; 54:172-178.

6.

Byung Ok Kwak et al:Microalbuminuria in mormal korean children. Yonsei Med Journal 2011; 52:476-481.

Anurag Singh and Simon C. Satchell:Microalbuminuria: causes and Implications. Pediatr Nephrol 2011; 26:1957-1965.

8.

Mahesh Bhattarai and Buna Bhandari: microalbuminuria in hypertension :A Review. Journal of Nobel Medical College 2012; 1:1-10.

9.

D Lad Hasit and KC Vasuda: A study of the levels of urinary microalbumin in nondiabetic normotensive obese individuals. Advances in Biological Chemistry 2012; 2:171175.

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10. SC Satchell and JE Tooke:what is the mechanism of microalbuminuria in diabetes: a role for the glomerular endothelium? Diabetologia 2008; 58:714-725.

11. Meng Lee Et al:Impact of microalbuminuria on incident stroke, a meta – analysis:Stroke. Journal of American Heart Association 2010; 41:2625-2631.

12. Amir Said Alizadeb and Robert F Reilly:primay care approach to Proteinuria. JABFM 2008; 21:569-574.

CHAPTER 29

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7.

C H A P T E R

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Early Identification of the Diabetic Nephropathy; Beyond Creatinine

INTRODUCTION

Diabetic nephropathy (DN) is the single most frequent cause of end-stage renal disease in the world and is the most common indication of haemodialysis. However, only about one third patient with diabetes develop nephropathy. It is characterized by microalbuminuria, subsequent macroalbuminuria, and declining glomerular filtration rate (GFR). An increasing number of type 2 diabetic patients live long enough for nephropathy and end-stage renal disease to develop because of the improvement in the treatment of diabetes, hypertension and coronary heart disease. Moreover, presence of stage 3 or higher chronic kidney disease (estimated GFR<60 mL/1.73m2) is associated with high cardiovascular mortality.

Accurate figures regarding prevalence of DN is lacking in India. Screening for DN is traditionally is being done by monitoring patients for the development of microalbuminuria, estimation of e-GFR, determination of serum creatinine (sCr), creatinine clearance (CCr), and nuclear scan. However, there are several limitations to these methods and search for ideal method is constantly being explored.

PATHOLOGY

It has been known since decades that the GFR is elevated in diabetes mellitus in early stages. Morphologically, the development of diabetic nephropathy is characterized by progressive thickening of the glomerular basement membrane and by expansion of the mesangial matrix which correlates to glomerular filtration function. The hallmark of diabetic glomerulopathy is diffuse mesangial expansion, associated with nodule formation in a minority of patients. Early hemodynamic changes of glomerular hyperperfusion and hyperfilteration are followed by leakage of albumin from the glomerular capillaries and structural changes such as glomerular basement membrane thickening, glomerular hypertrophy, glomerulosclerosis, mesangial cell expansion, and podocyte injury and loss.

CLINICAL FEATURES

Persistenting pedal and periorbital edema, decreasing urine output, increasing blood pressure in a diabetic patient are the features which should prompt physician to look for possible DN. In the initial phase increase in GFR due to glomerular hyperfiltration is common.

Persistent albuminuria (>300 mg/24 hr or 200 mg/min) is the hallmark of diabetic nephropathy, which can be diagnosed clinically if the following additional criteria

Vivek Pal Singh, S Avinash

are fulfilled: presence of diabetic retinopathy and the absence of clinical or laboratory evidence of other kidney or renal tract disease. Systemic hypertension ensues later.

This clinical definition of diabetic nephropathy is valid in both type 1 diabetes and type 2 diabetes. Absence of retinopathy almost rules out nephropathy in type 1 DM but in type 2 DM this chronology does not hold good in all cases.

SCREENINING AND DIAGNOSIS

Primary prevention of CKD, early detection of disease and prompt intervention with appropriate, evidence based measures will delay CKD onset and progression, improve kidney and cardiovascular outcomes, and reduce resources utilization. Despite these benefits, CKD is both under-diagnosed and undertreated, and awareness of CKD among both patients and providers is low. CKD is staged based on estimated glomerular filtration rate or eGFR. Detection of CKD in early stage gives treating physician great window of opportunity to preserve and protect kidney from further damage.

Screening of all diabetic patients for detection of nephropathy is mandatory. Several markers and methods are standardised over decades for detection of nephropathy and CKD. Measurement of serum creatinine, blood urea nitrogen, urinary albumin excretion, calculating the estimated GFR using creatinine clearance, inulin clearance and isotopic scans are used for either direct or indirect measure of kidney function. All these methods even though quite reliable, have several limitations. Most markers do not detect early nephropathy. Nuclear scan or Inulin clearance which can accurately detect GFR is either very expensive or cumbersome hence cannot be used in date to day practice. This brings us to the discussion of finding an ideal marker which can detect diabetic nephropathy in early stage.

MICRO & MACROALBUMINURIA

Albumin excretion up to 30mg/day is considered normal.

The earliest clinical evidence of DN is the appearance of low but abnormal levels (≥ 30 mg/day or 20 μg/min) of albumin in the urine, referred to as microalbuminuria, and patients with microalbuminuria are referred to as having incipient nephropathy. Microalbuminuria typically occurs after 5 years in type 1 diabetes. Without specific interventions, about 80% of subjects with type 1 diabetes who develop sustained microalbuminuria have their urinary albumin excretion increase at a rate of 10–20% per year to the stage of overt nephropathy or

clinical albuminuria (≥300 mg/24 h or ≥200 μg/min) over a period of 10–15 years, with hypertension also developing along the way. ESRD develops in 50% of type 1 diabetic individuals with overt nephropathy within 10 years and in >75% by 20 years.

National kidney Foundation and Kidney Disease Outcomes Quality Initiative (NKF: KDOQI) and professional bodies concerned with management of patient with diabetes recommend that all patients with type 2 Diabetes be screened annually for CKD, starting at diagnosis. Urinary albumin excretion should be evaluated either from 24 hour urine collection or from the albumin to creatinine ratio in a random spot sample. Because of fluctuations in urinary collection excretion, at least 2 of 3 samples collected within a 3 to 6 month time frame should be used to categorize the degree of albuminuria and avoid false positive results.

Measurement of albumin excretion in 24 hour urine and calculation of albumin and creatinine ratio in urine have been used with success in identifying patient who have microalbuminuria.

The limitations of estimation of microalbuminuria 1.

Evaluation of urinary albumin excretion alone is insufficient to assess the presence of and severity of CKD because some patients with type 2 diabetes can have advanced stage nephropathy in the absence of albuminuria i. e normo albuminuric DN.

2.

Few patients may have microalbuminuria but impaired renal function, but not the traditional decline of GFR with the development of proteinuria.

3.

Dose not detects DN in early stage (stage of hyperfiltration).

4.

Transient proteinuria like orthostatic proteinuria and overflow proteinuria as in case of multiple myeloma may interfere with the measurement of albuminuria.

5.

Few conditions other than diabetic nephropathy can cause excretion of albumin in urine in the range of 30-300mg/day. These include fever, high-salt diet, vigorous exercise, marked hyperglyceimia,

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NUCLEAR SCAN

Nuclear scan is considered gold standard in measuring GFR. The radioactive tracers are used for determination of GFR. Glomerular filtration rate and estimated renal perfusion flow may be assessed using dynamic quantitative nuclear imaging techniques. The GFR quantifies the amount of filtrate formed per minute (normal: 125 mL/min in adults).

Advantages of the Nuclear scan •

Most accurate method

•

Only method in which split GFR for each kidney can be obtained

•

Least influence of body weight and age

•

Helps in early detection of DN

Limitations of Nuclear Scan 1.

Complex procedure

2.

Needs specially trained individuals in handling and administering the tracers.

3.

Time consuming

4.

Expensive method, on an average cost of one DTPA scan is Rs. 4000 to 7000, in a resource poor set up, routine use of this method to determine kidney function is not practical.

5.

Radiation exposure to patient and individuals who are in close proximity to patient.

6.

Needs a dedicated nuclear scan centre with adequate measures to safely store radioactive compounds.

RENAL BIOPSY

Is one of the invasive means of knowing status of kidney in case traditional means dose not prove conclusive. Renal biopsy is certainly not indicated when a type 1 diabetic patient has retinopathy and when the time course is consistent with DN. Renal biopsy should be considered, however, when proteinuria is present less than 10 years after the onset of type 1 diabetes. In type 2 diabetes, this argument is unreliable because the onset of type 2 diabetes is often not known. The presence of dysmorphic erythrocytes, erythrocyte casts, or cellular casts is not a feature of DN and should prompt investigations to exclude glomerulonephritis or vasculitis, if necessary by renal biopsy. Other indications are rapid deterioration of renal function or elevated serum creatinine without urine abnormalities. Finally, gross proteinuria is not infrequently associated with non-diabetic renal disease, for example, amyloid, focal segmental glomerulosclerosis, etc. Needless to say that prior to renal biopsy renal ultrasonography is indicated which by itself may already yield a diagnosis.

Limitations of Renal biopsy 1.

Renal biopsy is used as an exception than a rule.

CHAPTER 30

Type 2 diabetes has a more variable course, higher proportion of individuals are found to have microalbuminuria and overt nephropathy at the time of diagnosis of their diabetes but fewer patients with microalbuminuria progress to advanced renal disease.

This is because, diabetes is actually present for many years before the diagnosis is made and also because the presence of albuminuria may be less specific for the presence of diabetic nephropathy, as shown by biopsy studies. Without specific interventions, 20–40% of type 2 diabetic patients with microalbuminuria progress to overt nephropathy, but by 20 years after onset of overt nephropathy, only about 20% will have progressed to ESRD.

uncontrolled hypertension, urinary tract infection and dehydration.

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2.

In contemporary practice renal biopsy is obsolete technique to diagnose nephropathy

3.

It is an invasive procedure and hence has all risks involved with invasive procedure.

4.

Not a practical method as a routine use.

NEPHROLOGY

ASSESSMENT OF FUNCTIONAL STATUS OF KIDNEYS USING EGFR

GFR is traditionally measured as the renal clearance of a particular indicator substance, or marker, from plasma.

The clearance of an indicator substance is the amount removed from plasma, divided by the average plasma concentration over the time of measurement.

Under the right conditions, measuring the amount of an indicator in both plasma and urine can allow the accurate calculation of GFR. Indeed, if we assume that there is no extrarenal elimination, tubular reabsorption, or tubular secretion of the marker, then GFR can be calculated as follows: Glomerular filtration rate = (U • V)/(P • T) (U is the urine concentration, V is the urine volume, and P is the average plasma concentration of the marker over the time (T) of the urine collection).

Unfortunately, tubular secretion, tubular reabsorption, or both, of the indicator can cause renal clearance measurements to give estimates of the GFR that are falsely high or falsely low. Under the right conditions, plasma concentrations of an indicator substance can be completely dependent on renal clearance and can accurately reflect GFR. When the amount of an indicator added to the plasma from an exogenous or endogenous source is constant, and when there is no extrarenal elimination, tubular secretion, or tubular reabsorption, then the GFR is equal to the inverse plasma concentration of the indicator multiplied by a constant.

Whether endogenous or exogenous, an ideal indicator would distribute freely and instantaneously throughout the extracellular space. It would not bind to plasma proteins and would be freely filtered at the glomerulus.

It would be subject to neither excretion nor reabsorption in the tubules or urinary collecting system. It would be completely resistant to degradation, and its elimination would be entirely dependent on glomerular filtration. It would be easy to measure in plasma and in urine, and nothing would interfere with the assay. Ideally, the interand intrapatient coefficient of variation would be low.

According to the KDOQI guidelines of the NKF, CKD will be stratified into the following stages based on eGFR: 1.

Stage 1: GFR ≥ 90 and Albumin excretion rate (AER) > 30mg per 24 hr.

2.

Stage 2: GFR 60-89 and AER >30mg per 24 hr.

3.

Stage 3: GFR 30-59.

4.

Stage 4: GFR 15-29.

5.

Stage 5: GFR < 15.

(All values of GFR are in ml/min/1.73m2 BSA) Hence accurate eGFR measurement gives us stage of CKD. Current markers recognize CKD when at least 5070% of nephrons in both kidneys are affected. Currently patients are diagnosed in stage 2 or 3 onwards where precious window of opportunity is lost to take necessary steps to either revert or slow the progression of CKD.

Inulin

Inulin, an inert substance was once considered the gold standard of exogenously administered markers of GFR. It does not bind to plasma proteins. It distributes in extracellular fluid, is freely filtered at the glomerulus, and is neither reabsorbed nor secreted by renal tubules. eGFR is measured by giving a loading dose of Inulin orally and urine samples are collected at regular interval after a steady state is achived. Currently this method carries only historical importance due to its high cost and complexity of the procedure.

Urea

Urea was one of the first indicators used to measure eGFR. Unfortunately, it shares few of the attributes of an ideal marker, and plasma urea has been shown to be a poor measure of GFR. Urea production is variable and is largely dependent on protein intake. Although one quarter of the urea produced is metabolized in the intestine, the ammonia produced is reconverted to urea. Thus, most of the urea is ultimately excreted by the kidneys. Because of tubular urea reabsorption, renal urea clearance usually underestimates GFR. Urea clearance can be as little as one half or less of the GFR as measured by other techniques.

Creatinine

Creatinine is a metabolic product of creatine and phosphocreatine, both of which are found almost exclusively in muscle. Thus, creatinine production is proportional to muscle mass and varies little from day to day. However, production can change over longer periods of time if there is a change in muscle mass. Age- and gender-associated differences in creatinine production are also largely attributable to differences in muscle mass.

Hence due to so many confounding factors creatinine levels may not give an accurate functional assessment of kidney function.

CREATININE CLEARANCE

Measuring creatinine clearance obviates some of the problems of using serum creatinine as a marker of GFR but creates others. Differences in steady-state creatinine production due to differences in muscle mass that affect serum creatinine does not affect creatinine clearance.

Extrarenal elimination of creatinine has little influence on the ability of the creatinine clearance to estimate GFR. However, the reliability of creatinine clearance is greatly diminished by variability in tubular secretion of creatinine and by the inability of most patients to accurately collect timed urine samples. The need to collect a urine sample remains a major limitation of the creatinine clearance technique.

CREATININE BASED EQUATIONS FOR MEASUREMENT OF EGFR

Many creatinine based mathematical equations have been formulated to calculate eGFR based on age weight and gender. Most extensively studied and validated among them are three: the Cockcroft and Gault(CG) equation, Modification of diet in renal disease equation (MDRD) and CKD Epidemiology equation. These have been corner stone of eGFR measurement in several studies and have been successfully replicated across poulations.

Limitations of Creatinine based formulas

Serum creatinine formulas to estimate the GFR may not be reliable in certain individuals. Individuals on a vegetarian diet, consuming creatinine supplements, with unusual muscle mass, with unusual weight (morbid obesity, amputation), or pregnant woman were not included in the study populations that were used to generate these formulas.

2.

These formulas are not accurate for individuals with normal or near-normal kidney function and ethnic groups.

3.

Among healthy individuals such as kidney donors, the MDRD formula underestimated GFR.

4.

In kidney transplant recipients, the MDRD provided variable results.

5.

For creatinine to raise beyond certain upper limit of normal at least 50-70% of nephrons should be damaged which gives little scope for early intervention and prevention.

Cockcroft-Gault Equation

eGFR= (140-age in years)×Body weight in Kg/72×serum creatinine (mg/dl) ×0.85 if female.

The Cockcroft-Gault equation is one of the most extensively used equation bedside to calculate eGFR. It estimates creatinine clearance in mL × min–1, but not GFR, and is not standardized to the body surface area of 1.73 m2. In relation to GFR it systematically overestimates clearance because tubular creatinine secretion is not taken into account. Because this equation includes body weight, it is particularly recommended for the monitoring of renal function during treatment with medications that influence kidney performance.

CYSTATIN C

min = The minimum of Scr/k or 1 max = The maximum of Scr/k or 1

Several low-molecular-weight (LMW) proteins have been evaluated as endogenous markers of GFR, with Cystatin C commanding the most attention. The use of serum Cystatin C as a marker of GFR was first suggested in 1985, when Simonsen and co-workers demonstrated a correlation between reciprocal Cystatin C values and 51Cr-labeled ethylenediaminetetraacetic acid (51CrEDTA) clearance. Since then, numerous investigators have shown that cystatin C may be a particularly good marker of GFR. Cystatin C is a 13-kD basic protein of the cystatin superfamily of cysteine proteinase inhibitors. It is synthesized by all nucleated cells at a constant rate, fulfilling an important criterion for any endogenous marker of GFR. In most studies, production of Cystatin C is not altered by inflammatory processes, by muscle mass, or by gender. An increase in levels of Cystatin C after the 5th decade reflects the age-related decline in GFR and contrasts with stable serum creatinine values, presumably due to a decline in muscle mass with age. Because of its low molecular weight and positive charge at physiologic pH, Cystatin C freely passes the glomerular filter. It is not secreted, but proximal tubular cells reabsorb and catabolize the filtered Cystatin C, resulting in very low urinary concentrations. Although calculation of GFR using urinary Cystatin C is not possible, some investigators have speculated that urinary Cystatin C could serve as a marker for renal tubular dysfunction.

The CKD-EPI creatinine equation is based on the same four variables as the MDRD Study equation, but uses a 2-slope “spline” to model the relationship between estimated GFR and serum creatinine, and a different relationship for age, sex and race. The equation was reported to perform better and with less bias than the MDRD Study equation, especially in patients with higher GFR. This results in reduced misclassification of CKD.

Studies in a number of patients have shown that serum Cystatin C may be more sensitive and specific than serum creatinine value for signifying early changes in isotopically determined GFR. ROC analysis of these studies demonstrated superiority of accuracy of Cystatin C over creatinine in patients with reduced GFR. In addition, small reductions in GFR appear to be detected more easily using cystatin C measurement than with creatinine

Modification of Diet in Renal diseases (MDRD) formula

eGFR = 186×(serum creatinine mg/dl)-1.154 × (age in years)-0.203

Multiplied by 0.742 if female and multiplied by 1.210 if African American The GFR has probably never been measured with more accuracy in a large population of patients than it was in the Modification of Diet in Renal Disease (MDRD) Study.

A simplified version requiring only serum creatinine value, age, race, and gender was found to similarly correlate with measured GFR. It was standardised mainly in patients with Stage 3 and higher stages and in patients on haemodialysis. This formula over estimates eGFR in early stages hence early CKD is undiagnosed.

CKD-EPI (creat) Formula

GFR - 141 X min(Scr/k, 1)α X max(Scr/k, i)-1.209 x 0.993Age X 1.018[if female] X 1.159 [if black] k

= 0.7 if female k k = 0.9 if male

α = -0.329 if female

α = -0.411 if male

CHAPTER 30

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NEPHROLOGY

160

determination. Other studies have indicated that cystatin C determination has a greater ability to detect subclinical kidney dysfunction than using creatinine measurement.

Coll and colleagues demonstrated that cystatin C levels rose when GFR fell to 88 mL/min/1.73 m2 and that creatinine levels did not rise until GFR dropped to 75 mL/min/1.73 m2. A meta-analysis incorporating studies published in 46 articles and 8 abstracts and using standard measures of GFR suggested superiority of reciprocal Cystatin Cvalue over reciprocal serum creatinine level as a marker of GFR. Cystatin C has also been examined in a diverse number of groups. In children, Cystatin C measurement appears to be at least as useful as serum creatinine determination in assessing GFR, although the number of children studied who were younger than 4 years is small. This age subgroup, for which serum creatinine levels have been unreliable, might arguably be most benefited by the measurement of Cystatin C to evaluate GFR. Cystatin C has been favourably evaluated in other similar subgroups, including patients with cirrhosis spinal cord injury, and rheumatoid arthritis, as well as elderly patients.

In kidney transplant recipients, Cystatin C value has been found to be more sensitive than serum creatinine level in detecting decreases in GFR. In one study, levels of Cystatin C were significantly higher in 54 pediatric kidney transplant recipients than in 56 control subjects with similar GFR values.

CYSTATIN C BASED FORMULAS:

Without exception all Cystatin C-based formulae were less biased than the MDRD formula with distinct 95% CIs being observed among these Cystatin C based CKD epidemiology equation is best studied. It includes correction based upon race, which makes it uniquely applicable to most of the races.

CKD-EPI Cys C formula

eGFR = 127.7×(Cystatin C in mg/L)-1.17 ×(age in years)-0.13 multiplied by0.91 if female.

With regard to accuracy, the proportion of estimated GFR results within 10% of isotopic GFR was greater using Cystatin C-based formulae than the MDRD formula, as evidenced by distinct 95% CIs. Avinash et al conducted one of the first ever comparative study of Cystain C based formulas in India in 2010.

A total of 172 subjects having diabetes were stratified into different CKD stages based on eGFR calculated using Cystatin C and creatinine based formulas. Both in albuminuric and non-albuminuric subjects, Cystatin C based formulas stratified more subjects in early CKD compared to creatinine based formulas.

Advantages of Cystatin C based eGFR over Creatinine based eGFR in different clinical settings: 1.

2.

In children: children have low levels cretinine and determination is unreliable in the lower range of measurement.

The Elderly: Owing to physiological reduction

in renal functional and decrease in muscle mass, Cystatin C correlates better than creatinine with inulin clearance.

3.

Myasthenic, leg amputees, paraplegics: Because of the lower muscle mass, creatinine synthesis is low and creatinine- based eGFR is late to detect renal failure.

4.

Diabetics: Early stages of renal failure are detected more reliabely with Cystatin C based than with creatinine based eGFR.

5.

Liver cirrhosis: Creatinine methods are slow to detect the decrease in GFR because metabolism in liver is reduced.

6. Cytostatic treatment: The nephrotoxicity of cisplatin is dose dependent and a reduction in GFR is detected erarlier by Cystatin C based than by creatinine based eGFR. 7. Contrast induced nephropathy: Cystatin C identified patients in early stages of CIN compared to creatinine. It is especially useful in case of patients undergoing Coronary angiography as these patients are already prone for acute kidney injury.

OTHER MARKERS OF KIDNEY INJURY

Studies have identified a relatively small number of genes that are specifically altered in acute renal tubule injury. The front-runners are genes, such as osteopontin, clusterin, Glutathione S-transferase α, neutrophil gelatinase– associated lipocalin (NGAL), kidney injury molecule-1 (Kim-1), tissue inhibitor of metalloproteinase-1 (TIMP1), interleukin 18 (IL-18). It has now become important to validate these as protein markers in urine and to confirm or refute their selectivity and sensitivity for use in preclinical studies and in disease states in humans.

Kim-1 is one of the best-characterized urinary biomarkers to date in both experimental animals and humans with renal disease.

In ischemic injury, Kim-1 expression is most prominent in the S3 segment in the corticomedullary region, which is the part of the nephron most susceptible to ischemic injury.

Kim-1 expression is also prominent in the midcortical and superficial tubules in renal disease models, where the primary insult is not directed to the S3 segment Kim-1 not only functions as a biomarker but also has predictive value for acute renal injury.

Beta 2 microglobulin

Beta 2 microglobulin is filtered by the glomeruli and reabsorbed by the proximal tubular cells where it is metabolized. Its plasma concentration increases with decreasing renal function. Beta 2 microglobulin was measured in several situations. And few studies have found it as a better marker than other.

Beta 2 microglobulin has been extensively studied in several studies and has been identified as an useful

marker but lacks large studies to use it as a regular marker of kidney disease.

Serum alfa-1 microglobulin, retinol binding protein, atrial natriuretic peptide, serum homocysteine have been tried with variable results.

As of now only serum creatinine and serum Cystatin C have been validated for clinical practice. Search for ideal and affordable marker is still on. Cystatin C being validated for eGFR measurement is a significant step forward. Early detection of kidney injury is possible with Cystatin C with least confounding variables.

1.

S Avinash, VP Singh, AK Agarwal, S Chatterjee, V Arya.

Identification and Stratification of Diabetic Kidney Disease Using Serum Cystatin C and Serum Creatinine Based Estimating Equations in Type 2 Diabetes: A Comparative Analysis. J Assoc Physicians India 2015; 63:28-35.

The American Diabetes Associationâ&#x20AC;&#x2122;s (ADA) evidencebased practice guidelines, standards, and related recommendations and documents for diabetes care.

Diabetes Care 2012; 35 Suppl 1:S1-S2.

3.

Coll E, Botey A, Alvarez L et al. Serum cystatin C as a new marker for noninvasive estimation of glomerular filtration rate and as a marker for early renal impairment. Am J Kidney Dis 2000; 36:29-34.

4.

KDOQI Clinical Practice Guidelines and Clinical Practice Recommendations for Diabetes and Chronic Kidney Disease. KDOQI. Am J Kidney Dis 2007; 49(2 Suppl 2):S12154.

5.

Rigalleau V, Beauvieux MC, Le MF et al. Cystatin C improves the diagnosis and stratification of chronic kidney disease, and the estimation of glomerular filtration rate in diabetes. Diabetes Metab 2008; 34:482-489.

161

CHAPTER 30

REFERENCES

2.

C H A P T E R

31

DEFINITION

Hematuria implies blood in the urine. If the urine is reddish to naked eye, it is called macroscopic hematuria and if blood is detectable only by microscopy it is called microscopic hematuria. Even one ml of blood in a litre of urine is enough to result in reddish urine. Microscopic hematuria is defined as presence of three or more red blood cells (RBCs) per high-power field. For urine analysis urine should be freshly voided, should be midstream, clean catch and not the first morning specimen. Urine samples collected following strenuous exercise, trauma, sexual intercourse, during febrile illness and during menstruation can show transient hematuria and hence be better avoided.

URINE TESTING

Analysis of urine should be performed as early as possible following collection. Dip stick is very sensitive and can detect microscopic hematuria of 1-5 RBCs/hpf with a sensitivity of 100 % & specificity of 99 %. The dipstick actually detects haemoglobin/ myoglobin and can show false positive results in case of hemoglobinuria and myoglobinuria. Therefore a positive dipstick reading merits microscopic examination for confirmation.A negative dip stick test virtually excludes hematuria.

One needs to keep in mind that in dilute urine (urine osmolality <308 mosm/l) RBCs lyse, thereby reducing the quantumof microscopic hematuria.

Significance of hematuria in patients following catheterization or on anticoagulant drugs

Studies performed by testing pre and post bladder catheterization urine samples for microscopic hematuria, revealed that a microscopic hematuria following catheter related urothelial trauma was indeed rare.

Likewise control studies of patients on anticoagulants also show that anticoagulants donâ&#x20AC;&#x2122;t increase the risk of hematuria. Hence it seems prudent not to outright neglect microhematuriain catheterised patients or those on anticoagulants. However exceptions can be there in patients with clotting or bleeding abnormality or difficult catheterizations.

Significance of Dysmorphic RBCs in differentiating upper or lower tract bleeding

Isomorphic RBC are normal dumbbell shaped and have smooth round outline. Their presence implies bleeding from lower tract. Dysmorphic RBCs (as name implies) are distorted, broken, less hemoglobinised. This change of shape occurs due to passage of RBCs through slit

Approach to Hematuria PP Varma, T Mohanty membranes of glomerulus and different osmolality. Some of these RBCs can be ring shaped with vesicle shaped protrusions on their surface and are called acanthocytes (G1 cells). Dysmorphic RBCs are best seen by phase contrast microscopy/ scanning microscope. Presence of dysmorphic RBCs is s/o glomerular origin however level of cut off required for dRBCs is not clear. In a study by Crop.et al, at a 40% cutoff point the sensitivity of urinary dRBC for excluding glomerular disease in patients with urological diseases was 100%,while still 78% of the patients with a glomerular cause of hematuria had less than 40% dRBC. None of the patients with proven urological disease showed dRBC above the cutoff of 40%. Another study suggests that presence of >80% dysmorphic RBC or presence of >5 % acanthocytes is highly suggestive of glomerular and >80% normal RBCs is suggestive of lower tract bleeding.

INCIDENCE AND ETIOLOGY

In five population based studies, the prevalence of asymptomatic hematuria varied from 0.19- 16.1%. This wide variation is due to difference in age, sex, amount of follow up and number of screening studies performed.

In older population with risk of urologic diseases the prevalence was as high as 21%.

Etiology of hematuria varies with age, sex and race.

Common causes of hematuria are: urinary tract infections, stones, BPH, trauma, tumours, cyst rupture etc. Glomerular diseases form an important cause of both macroscopic and microscopic hematuria.

In a study of 105 young men referred to a hospital with asymptomatic hematuria (mean age 24.8 years [range 18-53], 10% of the participants were > 40 yrs), 46.7% (49 patients) had abnormal findings; 24.8% had nephrological causes and in another 21.9% hematuria was of urologic origin.

In a study by Messing et al involving healthy males >50 yrs of age,1340Â men were screened at home for hematuria with dipstick. 21.1% had at least 1 episode of hematuria. Of the 192 hematuria positive men who received a complete urological evaluation, 16 (8.3%) had urological cancers and 47 (24.5%) had other hematuria-causing diseases that required immediate treatment.

In children between8 to 15 years, Bergstein et al observed microscopic hematuria in 4.1% of the participants and among adults the frequency of hematuria was reported between 2.4% to 31.1%; with higher rates in males over 60 yrs.

Table 1: Adult population (18-53 yrs) N= 105 Abnormalities

frequency

Glomerular Disease

26 (16.6%)

IgA nephropathy

16

PSGN

3

Thin basement membrane disease

2

MPGN

2

Interstitial nephritis

1

Urological Disease

23 (14.6%) 5

Trigonal Cystitis

5

Congenital Hydronephrosis

3

Urethral Stricture

3

Renal Scarring

3

Renal Calcifications

1

Cancer Of Renal Pelvis

1

Ureteric Stone

1

Bladder Cancer

1

Table 1 depicts the cause of asymptomatic microscopic hematuria as observed in an academic centre based study (involving referred patients).

Should all cases of asymptomatic microscopic hematuria be evaluated?

Hematuria without formed elements (blood cells casts) or proteinuria is called â&#x20AC;&#x153;isolated hematuria. In a study

by Ritchie et al, among the 76 patients with microscopic hematuria who underwent some further investigations (all investigations excepting cystoscopy), abnormalities were found in 21 (28%); and among those who were fully investigated by examination of midstream urine, intravenous urography, and cystoscopy, abnormalities were found in 12 (50%). These included bladder neoplasms (two), epithelial dysplasia (one), staghorn calculi (one), and chronic reflux nephropathy (one). Hence All subjects with asymptomatic microscopic hematuria should be investigated.

Role of kidney biopsy in asymptomatic microscopic hematuria

A Japanese study by Hoshino et al. on patients with asymptomatic hematuria found 62% of the participants to have IgA nephropathy while 13% had Thin Basement Membrane Disease. However, in the study methodology there was no mention of any urologic evaluation prior to the renal biopsy. Majority of these did not warrant any specific therapy. Hence the role of renal biopsy in the management of these patients is contentious. In another study on the long term outcome of asymptomatic microscopic hematuria, only 28 of the total 90 patients underwent renal biopsy- the most common finding was a normal glomerulus while the second and 3rd most common finding were thin basement membrane disease (9/28) and IgA nephropathy (8/28) respectively. After a mean follow up of 5 years only one patient developed CKD (after

Urologic evaluation principles1

All patients with asymptomatic microscopic hematuria require evaluation. In older individuals even transient hematuria should raise the suspicion of malignancy.

Hence, even a single episode of microscopic hematuria should prompt evaluation.

Radiologic evaluation is to be performed in all age groups. Following are the American Urology Association guidelinesFor Upper tract- (kidney +Pelvis & Ureter urothelium)-CT urography is recommended.

When CT is contraindicated in the patient, MR Urography can be done to delineate the upper urinary tract. When both CT and MRI are not possible, then USG and retrograde pyelogram may be performed for upper urinary tract evaluation.

For Lower tract (Bladder + Urethra) cystoscopy is the recommended modality.

Cystoscopy is also recommended in all patients >35 years of age or patients younger than 35 years but having risk factors for urothelial malignancy**.

Evaluation-includes evaluation of both upper and lower tract urothelium. **Risk Factors for Urinary Tract Malignancy Male gender, Age (> 35 years) Past or current H/O smoking, History of irritative voiding symptoms History of pelvic irradiation Occupational or other exposure to chemicals or dyes (benzenes or aromatic amines), Analgesic abuse, History of gross hematuria, History of urologic disorder or disease History of chronic urinary tract infection History of exposure to known carcinogenic agents or chemotherapy such as alkylating agents History of chronic indwelling foreign body In patients with persistent microhematuria following

163

CHAPTER 31

UTI

2.3 years). Interestingly 15 patients (17%) had complete resolution of hematuria. Hence, there is no consensus regarding the need and timing of renal biopsy in patients with asymptomatic microscopic hematuria. One can say that renal biopsy should not be the first investigation in these patients. We feel that all patients with isolated hematuria should be followed up. Those with persistent hematuria should have urological check. Renal biopsy should be resorted only if, hematuria is progressive or there is fresh appearance of proteinuria or renal functions are getting deranged.

An algorithm for hematuria is shown in Fig 1.

164 HEMATURIA

RULE OUT FEVER STRENUOUS EXERCISE MENSTRUATION

RECONFIRM

IF HEMATURIA STILL PERSISTS

NEPHROLOGY

DETAILED URINE ANALYSIS+USS

CYSTIC DISEASEeg ADPKD

REFER TO NEPHROLOGIST

ASSOCIATED WITH PROTEINURIA /RBC CASTS

STONE /OBSTRUCTION/ SOL

IF USS NEG

URINE PROTEIN TO CREATININE RATIO/DYSMORPHIC RBCS

URINE C/S POSITIVE

AGE >35 YRS

CT SCAN FOR STOENE

RISK OF MALIGNANCY

N

IF YES REFER TO NEPHROLOGIST FOR RENAL BIOPSY

ISOLATED HEMATURIA(NO OR MINIMAL PROTEIN)

H/O FLANK PAIN OR LOIN TO GROIN PAIN

PYURIA +

CULTURE POS

CULTURE REPEATEDLY NEG

UTI

LOOK FOR TB, STONE ETC

REFER TO UROLOGIST

6 MONTHLY FOLLOW UP (FOR HTN,↑CREAT & ↑PROTEINURIA

REFER TO UROLOGIST

Y UROLOGY REFERRAL FOR CYSTOSCOPY

REPEAT URINE R/E AFTER 6 WKS TO CONFIRM RESOLUTION

Fig. 1: An algorithm for hematuria of gross hematuria for urological cancers was found to be 0.22 while the same in people older than 40 yrs was 0.44. According to AUA any adult with gross hematuria must receive a complete evaluation (CT Urography and Cystoscopy) for urological malignancy irrespective of Follow up of patients with a negative urologic workup age. There are only five glomerular conditions which can Conclusion For persistent asymptomatic microhematuria after cause gross hematuria-IgA nephropathy, post infectious negative urologic work up, yearly urinalyses should be glomerulonephritis, pauciimmune glomerulonephritis, Microscopic is aor common urinary abnormality across all age groups. Etiology conducted. hematuria For persistent recurrent asymptomatic Alport’s Syndrome and thin basement membrane disease. microhematuria after initial negative urologic work-up, varies with age and sexthree but toInfections, stonebedisease andTO prostate related diseases are repeat evaluation within five years should APPROACH A CASE OF MICROSCOPIC HEMATURIA considered.

Step 1 a negative work up or those with other risk factors for carcinoma in situ (e.g.irritative voiding symptoms, current or past tobacco use, chemical exposures) urine cytology may be useful.

dominant causes. Patients with proteinuria, freshly diagnosed hypertension or deranged renal Confirm presence of hematuria.

Fever, mensturation, Approach to gross hematuria

exercise etc are common causes of transient hematuria.

The approach gross hematuria remains practically functions have to generally an identifiable causetheandUrine needshould renal be biopsy. with retestedEvery after patient fever/ mensturation

same as that to microscopic hematuria. The only difference is that here the emphasis shifts to urological causes from subsides. persistent hematuria needs thorough evaluation.

Despite thorough evaluation a large the glomerular causes. In a study in pediatric population Scenario 1 2/4 th ofstill the remain participants were found and to have urologic proportion undiagnosed need periodic followhasup.

If patient dysuria, fever, increased frequency and urine causes,1/4th had glomerular causes and in ¼ th the cause shows WBCs/WBC casts- urine culture should be done remained undiagnosed. Buntinx et al performed a meta- and patient be treated with suitable antibiotics on lines analysis to find out the diagnostic value of gross hematuria. of UTI. A positive urine culture confirms the diagnosis Most of the studies included only adults. The pooled PPV of UTI. However, a negative urine culture does not rule

out the same because administration of antibiotics rapidly makes the urine culture sterile. However, if the suspicion of UTI is clinically low, then the patient should be evaluated for sterile pyuria which involves both urologic (for stone/tumor/genitourinary TB) and nephrology (acute interstitial nephritis) work up.

biopsy. Every patient with persistent hematuria needs thorough evaluation. Despite thorough evaluation a large proportion still remain undiagnosed and need periodic follow up.

REFERENCES

If patient has flank pain or pain radiating from loin to groin, s/o nephrolithiasis, patients be subjected to USS/CT scan and referred to urologist. Recurrent stone formers should undergo metabolic evaluation. CT is much better modality for picking stone vis a vis USS.

Davis R, Jones JS, Barocas DA, Castle EP, Lang EK, Leveillee RJ, et al. Diagnosis, evaluation and follow-up of asymptomatic microhematuria (AMH) in adults: AUA guideline. The Journal of Urology 2012; 188(6 Suppl):2473-81.

2.

Scenario 3

Vehaskari VM, Rapola J, Koskimies O, Savilahti E, Vilska J, Hallman N. Microscopic hematuria in school children: epidemiology and clinicopathologic evaluation. The Journal of Pediatrics 1979; 95(5 Pt 1):676-84.

3.

Messing EM, Young TB, Hunt VB, Roecker EB, Vaillancourt AM, Hisgen WJ, et al. Home screening for hematuria: results of a multiclinic study. The Journal of Urology 1992; 148(2 Pt 1):289-92.

4.

Sparwasser C, Cimniak HU, Treiber U, Pust RA. Significance of the evaluation of asymptomatic microscopic haematuria in young men. British Journal of Urology 1994; 74:723-9.

5.

Sklar DP, Diven B, Jones J. Incidence and magnitude of catheter-induced hematuria. The American Journal of Emergency Medicine 1986; 4:14-6.

If patient has isolated hematuria or insignificant proteinuria (< 500 mg) and USS is normal. One should exclude urology cause. Many such patients have underlying IgA nephropathy or thin basement membrane disease or Alportâ&#x20AC;&#x2122;s Syndrome and are unlikely to require any specific treatment even when diagnosed. Kidney biopsy in this setting is contentious and such patients need to be followed up periodically.

6.

Hockberger RS, Schwartz B, Connor J. Hematuria induced by urethral catheterization. Annals of Emergency Medicine 1987; 16:550-2.

7.

Ritchie CD, Bevan EA, Collier SJ. Importance of occult haematuria found at screening. British Medical Journal (Clinical Research Ed) 1986; 292:681-3.

8.

CONCLUSION

Crop MJ, de Rijke YB, Verhagen PC, Cransberg K, Zietse R. Diagnostic value of urinary dysmorphic erythrocytes in clinical practice. Nephron Clinical Practice 2010; 115:c203-12.

9.

Hoshino Y, Kaga T, Abe Y, Endo M, Wakai S, Tsuchiya K, et al. Renal biopsy findings and clinical indicators of patients with hematuria without overt proteinuria. Clinical and Experimental Nephrology 2015; 19:918-24.

If patient is passing blood clots, it is most likely a urological problem e.g. bladder tumour, trauma, bladder stone etc. and patient needs referral to urologist.

Scenario 4

If urine shows dysmorphic RBCs, proteinuria, RBC casts etc. glomerular pathology is likely. A proteinuria of >2 gm is s/o glomerular pathology and such patients need renal biopsy and should be referred to Nephrologist.

Scenario 5

Microscopic hematuria is a common urinary abnormality across all age groups. Etiology varies with age and sex but Infections, stone disease and prostate related diseases are dominant causes. Patients with proteinuria, freshly diagnosed hypertension or deranged renal functions have generally an identifiable cause and need renal

10. Chow KM, Kwan BC, Li PK, Szeto CC. Asymptomatic isolated microscopic haematuria: long-term follow-up.

QJM : monthly Journal of the Association of Physicians.

2004; 97:739-45.

CHAPTER 31

1.

Scenario 2

165