Does urinary metabolic assessment in idiopathic calcium nephrolithiasis matter? A matched case control study among Indian siblings

Objective: To identify the differences in urinary profile of a stone former and the matched member of the family.
Patients and Methods: This prospective case-control study was conducted from April 2006 to January 2008. Forty-one matched pairs from one geographic region were recruited. Renal/ureteric idiopathic calcium nephrolithiasis in patients of 18 years and above were included as cases. Controls were of the same gender and first-degree relative with no urolithiasis or history. They were living together at least for the last 5 years and consuming minimum of two out of three major meals together per day. For cases and controls besides fluid intake, ambulatory serum analysis for calcium, phosphorus, uric acid, albumin-globulin ratio, sodium, potassium and bicarbonate was done. Ambulatory 24-hour urinalysis was done for urinary volume, calcium, phosphorus, oxalate, uric acid, citrate, magnesium, creatinine and urinary pH was measured. For controls X-ray and USG-Kidney-Ureter-Bladder was done to rule out stone disease. The statistical analysis was done using Mc-Nemar test.
Results: Of the 41, 31 cases (76%) were first-time stone formers. No statistical difference was found for 24-hour urinary calcium (P = 0.68), oxalate (P = 0.68), citrate (P = 0.45) and urinary volume (P = 0.14). All pairs had normal 24-hour urinary magnesium, uric acid and urinary pH.
Conclusions: The urinary biochemical profile of idiopathic calcium nephrolithiasis was similar to the appropriately matched family member. It appears that an independent intrinsic factor may possibly be present and responsible for stone disease. The usefulness of urinary metabolic evaluation is seems to be of doubtful significance.