MKSAP Quiz: kidney stone prevention
Disclosing medical errors does not increase malpractice claims
A 22-year-old woman comes for a routine office visit. Medical history is insignificant, and she takes no medications. Her father and brother have kidney stones caused by high levels of urine calcium. She has increased her fluid intake.
On physical examination, vital signs are normal. BMI is 27.
Laboratory studies:
Which of the following is the most appropriate next step in this patient's management?
A. Add a calcium supplement
B. Decrease dietary animal protein intake
C. Increase dietary calcium intake
D. Increase dietary sucrose intake
MKSAP Answer and Critique
The correct answer is C) Increase dietary calcium intake. This item is available to MKSAP 15 subscribers as item 57 in the Nephrology module.
An estimated 33% of patients with kidney stones have a family history of stone formation, and most of these stones are caused by hypercalciuria. This patient is therefore at increased risk for stone formation, and the most appropriate next step in management is an increase in her dietary calcium intake. Calcium oxalate stones can develop when calcium binds to oxalate in the urine. Adherence to a high-calcium diet (generally defined as 1 to 4 g/d of calcium) has been shown to decrease the risk of calcium oxalate stone formation by binding calcium to oxalate in the gut and preventing oxalate absorption and its filtration into the urine.
Calcium supplementation in addition to or in place of increased dietary calcium intake has not been shown to decrease the risk of kidney stone formation. Furthermore, calcium carbonate supplementation with meals may be associated with slightly increased rates of stone formation.
Animal protein intake contributes to increased purine metabolism and uric acid production and has been associated with uric acid stone formation. Animal protein ingestion also leads to decreases in urine citrate and increases in urine calcium. In a randomized, controlled trial to prevent stone formation, a diet with increased calcium content and reduced animal protein and salt was shown to effectively decrease stone recurrence in men with hypercalciuria compared with a reduced-calcium diet; however, this intervention has not been shown to prevent the incidence of calcium stones in women, and a low-protein diet alone has not been shown to reduce calcium stone formation in either men or women.
Increased dietary intake of sucrose appears to increase urine calcium excretion independent of calcium intake and has been shown to increase the risk of incident kidney stones in women. This intervention would not be recommended for a patient at risk for stone formation.
Key Point
- Adherence to a high-calcium diet (generally defined as 1 to 4 g of calcium per day) has been shown to decrease the risk of incident and recurrent calcium oxalate stone formation.