CKD with Albuminuria — USMLE Step 2 CK MCQ

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ModerateNephrologyCKD with AlbuminuriaUSMLE Step 2 CK

A 48-year-old man has passed three calcium oxalate stones during the past 2 years despite achieving a urine volume above 2.5 L/day. Two 24-hour urine collections show persistent hypercalciuria with normal urinary uric acid and citrate. Serum calcium and parathyroid hormone are normal. Which additional preventive strategy is most appropriate?

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Correct answer: E — Begin a thiazide diuretic and reduce dietary sodium

Recurrent calcium stones with persistent hypercalciuria despite adequate urine volume are an indication for a thiazide diuretic. Thiazides lower urinary calcium, and dietary sodium restriction improves the hypocalciuric effect while reducing potassium loss. Follow-up should assess electrolytes, adverse effects, urine chemistries, and stone activity. Allopurinol is used for selected recurrent calcium oxalate stone formers with hyperuricosuria and normal urinary calcium, which is not this patient's profile. Loop diuretics increase urinary calcium and can worsen risk. Severe dietary calcium restriction is counterproductive because normal dietary calcium binds intestinal oxalate; restriction may increase oxalate absorption and jeopardize bone health. High fluid intake should continue to maintain urine volume above approximately 2.5 L/day. Other dietary measures include moderating animal protein and maintaining normal food-based calcium intake.

Reference: American Urological Association. Medical Management of Kidney Stones. https://www.auanet.org/documents/Guidelines/PDF/clinical-guidance/Medical-Management-of-Kidney-Stones.pdf ; NIDDK. Eating, Diet, and Nutrition for Kidney Stones. https://www.niddk.nih.gov/health-information/urologic-diseases/kidney-stones/eating-diet-nutrition