Case Study: Renal calculi

by Dr Fred Pender Dietitian and Author

Dr Fred Pender is a dietitian with over thirty years experience both as an academic and a practitioner. An enthusiatic exponent of the case-based approach as a method of teaching dietetics, he believes that it is an important vehicle for bringing practice into the classroom.

Obesity, renal calculi

Study concepts: lifestyle issues associated with management of renal calculi Study context: kidney stones, obesity

Mr Tony Marshall has a history of kidney stones and recently failed a medical routinely performed by the occupational health department. He has raised levels of uric acid and may have a small renal stone currently. He has recently celebrated his 50th birthday with family and friends. He is a long-haul airline pilot.

Tony has been a heavy drinker in the past and LFTs have revealed a somewhat damaged liver. He has been trying to self-limit his calcium intake with respect to his kidney stones as a result of going on a website he found on the internet. He is currently 103kg (5ft 11in). He likes his food, confesses to eating very large portions, especially of salty/high fat foods and snacks and reports that his favourite foods include cheddar cheese, milk (full fat) and pizzas. He is referred to the dietitian.

Questions to consider 1. Explain what the therapeutic plan might be for Mr Marshall in managing his weight. 2. Comment fully on how his occupation and love of food might complicate dietary adherence. 3. Explain the extent to which it may be useful to consider managing his history of kidney stones by diet and/or lifestyle. 4. Assuming intervention takes the form of general dietary advice, what particular aspects of the information may be important and why? 5. Assume he comes back to clinic for review, say in eight weeks, and has lost 5kg. Consider the key points that may be useful to consider at the review appointment interview.

Study questions 1. Review the evidence implicating diet and lifestyle in the risk associated with development of renal calculi. Comment on the weight of evidence and how this may affect diet and lifestyle priorities in this case. 2. Comment fully on the extent to which faulty snacking behaviour may be associated with the onset of overweight and obesity. 3. Consider the role of both intake of fluid and NSPs in the therapeutic management of this case. What might be their role in the long-term management?

Commentary

The case presents the picture of an obese client with a history of raised uric acid levels. The client has been motivated to seek help via the internet to reduce his risk of stones, but he needs to lose weight and adopt a more scientific approach to manage his risk of developing more stones. He is likely to have a high intake of protein and salt (two factors which assist calcium excretion and therefore enhance stone-forming risk) together with a high intake of. purines (meat). Whilst 80 per cent of stones contain calcium, there is no real evidence that dietary restriction reduces risk of stone development. The effects of dietary intervention on the reduction of the risk of developing are likely to be small, but perhaps worthwhile to consider. The client is likely to be maintained using appropriate drug intervention (allopurinol).

Whilst the client may be at cardiovascular risk, initial assessment should concentrate on dietary (diet history or diet diary) and lifestyle (exercise, intake of alcohol and salt) assessment. Weight parameters may be noted with a view to monitoring from baseline and calculation of energy requirements.

Short-term goals include implementing dietary changes to reduce the risk of formation of stones and for general health improvement (healthy eating and to encourage weight loss and improve cardiovascular health). Implementation of an energy-deficit intake, based on healthy eating (high in starchy carbohydrate and lower in fat) with particular focus on reducing protein and salt intake will assist in achieving weight loss and reAn extract from Clinical Cases in Dietetics

duction in the risk of formation of stones. The dietary intake may be centred on an energy prescription based on: BMR: (103 x 11.6) + 879 = 2074kcal; in addition to a PAL factor (light activity) = 2074 x 1.55 = 3214kcal together with an energy deficit of 5-700kcal = 2500-2700kcal/d. The intake should be planned to include salt restriction (probably to the level of NAS, or 80-100mmol/d), alcohol restriction to recommended levels and protein modification to about 1g/kg/d (to reduce exposure to both protein and purines). An emphasis on greater intake of NSPs will be useful (stone formation is less likely with cereal/vegetable-based protein intakes). The client must not be encouraged to have oily fish (high in purine content) and should switch to lower fat dairy products. Approaches must focus on reducing portion sizes, especially of protein containing foods. Fluid intake should be increased to about two litres to three litres per day to promote production of dilute urine.

In the longer term, issues include general health improvement via diet and lifestyle improvement, including engagement in light sustained physical exercise. Monitoring should include weight parameters and dietary compliance, especially with regard to protein and salt intake. The client may be monitored frequently in the first instance (every eight to 10 weeks) and thereafter revert to the care of either a practice nurse or occupational health nurse. Cardiovascular parameters may be worth exploring in the context of general health, with dietary and lifestyle reinforcement as necessary.