Differences in quantitative urine composition in stone-forming versus unaffected mate kidneys

OBJECTIVES Many patients present with bilateral stones. There is a unique group of patients, however, that presents with stones exclusively on one side. We hypothesize that in such situations, 24-hour urine collections may not reveal specific defects on the affected stone-bearing kidney. We therefore evaluated selective 12-hour urine collections after percutaneous nephrolithotomy (PNL) to help determine if there is differential renal excretion. METHODS We collected urine specimens from patients with nephrolithiasis who underwent unilateral PNL. Urine samples were collected and analyzed from nephrostomy tubes, representing the affected kidneys, and from Foley bladder catheters, representing the contralateral mate kidney. RESULTS Thirty-one patients were studied (14 with unilateral nephrolithiasis and 17 with bilateral). Treated kidneys from patients with unilateral nephrolithiasis displayed lowered urine excretion of uric acid, sodium, chloride, calcium, and total osmoles when compared to patients with bilateral nephrolithiasis. Stone size and length of procedure were not predictive of urine composition after PNL. CONCLUSIONS Treated kidneys from patients with a history of unilateral stone disease revealed marked differences in urine excretion compared to those with bilateral nephrolithiasis after unilateral PNL. These findings could be secondary to the surgical insult, urinary stone disease, or could be a responsible factor for stone pathogenesis.