What is the role of citrate and magnesium measurement in the diagnosis of nephrolithiasis?

Updated: Jan 13, 2020
  • Author: Chirag N Dave, MD; Chief Editor: Bradley Fields Schwartz, DO, FACS  more...
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Magnesium and, especially, citrate are important chemical inhibitors of stone formation. Hypocitraturia is one of the most common metabolic defects that predispose to stone formation, and some authorities have recommended citrate therapy as primary or adjunctive therapy to almost all patients who have formed recurrent calcium-containing stones.

Many laboratories use 24-hour urine citrate levels of 320 mg/d as the normal threshold, but optimal levels are probably closer to the median level (640 mg/d) in healthy individuals. Periodic monitoring of pH with pH test strips can be very useful to titrate and optimize citrate supplementation. A pH level of 6.5 is usually considered optimal. A pH level over 7.0 should be discouraged, as it prompts calcium phosphate precipitation.

Potassium citrate is the preferred type of pharmacologic citrate supplement, though a potassium/magnesium preparation is under investigation. Liquid or powder pharmacologic citrate preparations are recommended when absorption is a problem or in cases involving chronic diarrhea. Sustained-release tablets are available and may be more convenient for some patients. Lemon juice is an excellent source of citrate; alternatively, large quantities of lemonade can be ingested, and this, of course, has the added benefit of providing increased fluid intake.

Magnesium is a more recently recognized inhibitor of stone formation, and the clinical role of magnesium replacement therapy is less well defined than that of citrate.

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