Adequacy of a single stone risk analysis in the medical evaluation of urolithiasis

Purpose: We tested the hypothesis that a single 24-hour urine sample for stone risk analysis would be sufficient for the simplified medical evaluation of urolithiasis. Materials and Methods: We retrospectively analyzed stone risk profile data on 24-hour urine samples obtained during random and restricted diets in 225 patients with recurrent urolithiasis. Results: In 2 random samples we noted no significant difference in urinary calcium, oxalate, uric acid, citrate, pH, total volume, sodium, potassium, sulfate or phosphorus. For these risk factors there was a highly significant positive correlation in the 2 random samples (r greater than or equal to0.68, p <0.0003) and the value of each was abnormal or normal in at least 81% of patients. Urinary magnesium and ammonium were significantly lower in random sample 2 than 1, the former by 4%. After calcium, sodium and oxalate dietary restriction mean urinary calcium and sodium plus or minus standard deviation decreased significantly by 25% from 251 +/- 125 to 187 +/- 98 mg. daily and by 38% from 183 +/- 87 to 113 +/- 57 mEq. daily, respectively. Other risk factors had a slight or no significant change. Correcting random urinary calcium for the excessive urinary excretion of sodium brought urinary calcium to 210 +/- 108 mg. daily, similar to the value on the restricted diet. Conclusions: The reproducibility of urinary stone risk factors is satisfactory in repeat urine samples. A single stone risk analysis is sufficient for the simplified medical evaluation of urolithiasis.