UCSF

Objectives

Urinary excretion of citrate is dependent on glomerular filtration, tubular reabsorption, and excretion. Acid base status is thought to play a significant role in urinary citrate excretion. It has been assumed that increased urinary citrate will increase urinary pH. The aim of this study was to confirm the association of increased urinary citrate levels with increased urinary pH.

Methods

The 24-hour urine collections of all patients with stones referred to our clinic in the past 4 years were reviewed. The samples were collected and analyzed for routine stone risk profiles by a commercial laboratory (Litholink, Chicago, Ill). The Student t test and analysis of variance were used to compare the mean values as applicable. Pearson's correlations were also calculated for each variable.

Results

A total of 572 patients had at least one 24-hour urine sample from the past 4 years. The mean urinary citrate was 305 mg/day. The mean urinary pH of all patients was 6.14. Statistical evaluation of all patients showed no correlation between urinary citrate and pH (r = -0.04, P = 0.36). In a subset of patients with urinary potassium greater than 100 mEq/day (n = 100), urinary citrate and urinary pH were both increased; however, there was still no correlation between the two (r = 0.011, P = 0.806).

Conclusions

Despite the current dogma that increasing urinary citrate increases urinary pH, in a cohort of patients with urinary stone formation who provided 24-hour urine specimens, no correlation was found between urinary citrate and urinary pH levels.