Test Summary

This quantitative citric acid test, performed with a random urine specimen, may help assess the risk of calcium stone formation in the kidneys and inform patient management [1]. In general, 24-hour urine specimens (Citric Acid, 24-Hour Urine with Creatinine) are preferred to random urine specimens when measuring citric acid for diagnostic evaluation and monitoring of calcium nephrolithiasis [2].

Citrate inhibits calcium stone formation by binding and solubilizing calcium, which reduces supersaturation of calcium salts [1-2]. Approximately half of the patients with calcium stones have decreased urinary citrate levels [1]. Citrate is among several substances routinely screened to evaluate the risk of forming kidney stones. Low urinary citrate levels may indicate oral citrate treatment in patients with recurrent calcium nephrolithiasis [1]. Other conditions that can cause hypocitraturia include distal renal tubular acidosis, malabsorption, and urinary tract infection [1].

The urinary citric acid level cannot be used to estimate dietary intake because other factors, such as acid-base balance, may affect citrate excretion [2].

The results of this test should be interpreted in the context of pertinent clinical and family history and physical examination findings.

References
1. Delaney, PM et al. Kidney disease. In: Rifai R, et al. eds. Tietz Textbook of Laboratory Medicine. 7th ed. Elsevier Inc; 2022.
2. Williams JC Jr, et al. Urolithiasis. 2021;49(1):1-16.

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