Urinary citrate in kidney stone disease.

Area of Science:

• Nephrology
• Urology
• Biochemistry

Background:

• Hypocitraturia (low urinary citrate) is a known risk factor for nephrolithiasis (kidney stones).
• Urinary citrate levels are influenced by acid-base balance, but metabolic acidosis is not always evident in stone patients with hypocitraturia.
• This study investigated the incidence and causes of hypocitraturia in stone patients lacking obvious acid-base imbalances.

Purpose of the Study:

• To estimate the incidence of hypocitraturia in a cohort of kidney stone patients.
• To identify potential causes of hypocitraturia, particularly in the absence of overt metabolic acidosis.
• To explore the role of gastrointestinal alkali absorption in hypocitraturia.

Main Methods:

• Analysis of 24-hour urine chemistry from 310 kidney stone patients on regular diets, with multiple measurements per patient (1361 specimens total).
• Calculation of net gastrointestinal alkali absorption using 24-hour urine chemical data in patients with unexplained hypocitraturia.
• Comparison of gastrointestinal alkali absorption between hypocitraturic patients and a normal control group.

Main Results:

• Hypocitraturia was identified in 38.4% of the 310 patients studied.
• Among 222 patients with calcium stones, 31.5% exhibited hypocitraturia.
• Patients with hypocitraturia and no apparent cause showed significantly lower net gastrointestinal alkali absorption compared to controls (9.2 vs. 34.4).

Conclusions:

• Defective gastrointestinal alkali absorption is a potential contributing factor to hypocitraturia in calcium stone patients.
• This finding suggests a non-acid-base related mechanism for hypocitraturia in a subset of kidney stone formers.
• Further research into gastrointestinal function may be warranted for managing hypocitraturia and preventing kidney stones.