A recently published study showed no correlation between urinary pH and citrate concentration.
The established practice for preventing urinary calculi is being challenged by results of a recent study (Whitson et al, Urology. 2007;70:634-637), which showed no correlation between urinary citrate levels and urinary pH. The study authors found that calcium citrate has been commonly prescribed as a stone inhibitor with benefit attributed to the prevention of calcium-oxalate deposits, diminished growth of calcium-oxalate crystals, and urine alkalinization.
Despite the prevalence of kidney stones, an understanding of etiologic factors and best preventive treatments remain subjects of investigation. Acknowledging the need for quality evidence regarding use of potassium citrate (Urocrit-K) to diminish calcium oxalate stone risk, the American Academy of Family Physicians (Am Fam Physician. 2006;74:86-94, 99-100) has given it an evidence rating of “B” (“inconsistent or limited-quality patient-oriented evidence”). This is based on the “findings from one randomized trial and usual clinical practice.”
To clarify inconsistencies in previous studies regarding the possible relationship of citrate supplementation to urinary pH in stone prevention, Whitson et al examined 24-hour urine collections from 572 outpatients who had been referred for stones during the four-year period from 2001-2005. Along with comparing urinary citrate to urinary pH, the study also looked at its potential relationship to age, gender, urine volume, and prescribed medications (allopurinol, alkalinization, hydrochlorothiazide). Subgroup analysis also included assessing associations between self-reported compliance and potassium citrate use as verified by urinary potassium level.
Significant study results reported by Whitson et al include:
- No correlation between urinary pH and citrate concentration.
- Lack of citrate, pH correlation when stratified by age, gender, or urine volume.
- No correlation with urinary pH and urinary citrate in self-reported supplemental potassium citrate users (urinary potassium greater than 100 mEq).
The authors hypothesize that global acid-base balance drives urinary pH, and based on study results conclude that “urinary citrate is not a primary determinant of urinary pH, regardless of supplementation status.” Recognizing the limitations of this retrospective study, the authors plan “a prospective study of urine collections obtained from patients with nephrolithiasis both before the first initiation of citrate therapy and at defined intervals during therapy, which will allow us to characterize in more detail the relationship between urinary citrate and urinary pH.”