Urinary citrate in kidney stone disease.

BACKGROUND Hypocitraturia, or low urinary citrate excretion is known as a risk for nephrolithiasis. Though urinary citrate excretion is basically determined by acid-base balance, metabolic acidosis is not always manifest in urinary stone patients with hypocitraturia. From our stone clinic data, we estimated the incidence of hypocitraturia and addressed its causes in the absence of obvious acid-base imbalance. METHODS We selected 310 stone patients in whom 24-hour urine chemistry was examined on regular diets on 2 or more occasions during follow-up. Totally, 1361 specimens were analyzed in them. RESULTS In the male subjects, the average urinary citrate excretion was 450.9 +/- 284.4 mg/ day, whereas in the female, 536.5 +/- 305.9 mg/day (p < 0.0001). Eventually, hypocitraturia was found in 119 of the 310 patients (38.4 %). Of 222 with calcium stones, 70 (31.5 %) had hypocitraturia. In 32 of those, potential causes of hypocitraturia were identified, but in the rest, no apparent cause was found. In the latter, the net gastrointestinal alkali absorption was calculated from the 24-hour urine chemical data, and it was lower in those with hypocitraturia than in the normal control (9.2 vs. 34.4). CONCLUSION It was suggested that defective gastrointestinal alkali absorption may be involved in hypocitraturia of calcium stone patients.