Introduction to Chemical Pathology 1) List the five common diagnostic tests carried out by the department of chemical pathology 1. 2. 3. 4.
Electrolytes – (including Na and K) Urea & Creatinine – high levels suggest renal failure Calcium & Phosphate – measure of bone LFT (Liver Function tests) • • • •
A measure of liver enzymes. Damage to the liver results in extra liver enzymes leaking into the blood. Particular diseases are associated with particular patterns of enzyme leakage. Enzymes commonly measured include: Alkaline phosphatase Aspartate amino-transferase (AST) Alanine amino-transferase (ALT) Gamma glutamyl transferase (GGT) 5. Hormone assays – done as a sub-division of chemical path. Hormones commonly measured include thyroxine, TSH and cortisol 6. Glucose – can be reapidly measured using a glucose sensitive stick on the ward or home. A more sensitive measurement is made in the lab. • Red cells will consume glucose (anaerobic glycolysis), even after it is out of the patient, unless they are poisoned: • Fluoride oxalate is used for this purpose. 2) Know how to collect specimens for common tests including electrolytes, urea, glucose and glycosylated haemoglobin
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When collecting blood… Make sure you use the right bottle If you get it wrong throw it away and start again Make sure you get the correct patient Label the tube correctly with the patients name If it is urgent ensure it gets to the lab in time
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Different tubes have different anticoagulants and so have different samples:
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Bottle Colour Red Yellow (orange) Purple Green Grey Turquoise
Contains None Gel to speed up clot Potassium EDTA Lithium Heparin Fluoride oxalate (poison) Citrate (anti-coag)
Test U&E, TFT, LFTs U&E, TFT, LFTs HbA1c Homocysteine Glucose Clotting factors
No anticoagulant (red/yellow) – for U&E, the blood clots using up all clotting factors, this can then be removed leaving the serum which is needed • Anticoagulant – EDTA or heparin, the clotting factors are unused so the blood can be separated into red cells and plasma – the two components which are needed • Measuring glucose – red cells consume glucose so the longer this is left out the more glucose is used. Fluoride oxalate in the grey topped bottles kills the cells – preventing glucose use •
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A chemical pathologist in the lab needs to be contacted if: You want the sample rapidly centrifuged out of hours
To measure labile hormones such as insulin When CSF (spinal tap) glucose and protein is needed to be urgently measured
3) Describe a typical chemical pathology request form
Cardiac enzymes: • •
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Are present in the heart muscle Leak out during MI Troponins Creatine Kinase (CK) Apartate amino transferase (AST) Lactate dehydrogenase (LDH)
Normal Ranges: Na = 135-145mM/L K = 3.5-5mM/L Creatinine = 70-150µmol/L Urea = 2.5-6.7mmol/L Proteins = 60-80g/L Calcium = 2.12-2.65mmol/L