Introduction: Urinary citrate is thought to decrease calcium stone formation through direct inhibition of crystallization and by complexing with calcium. A subset of nephrolithiasis patients excrete very high amounts of citrate with unclear clinical implications. Here we sought to profile nephrolithiasis patients with urinary citrate wasting.
Methods: We identified 2,257 consecutive patients who underwent 24-hour urine studies performed at our institution from 2001 to 2017. We identified patients with 1st time urine testing with citrate wasting, defined as >1500 mg/day. Patients were excluded if on any alkali therapy. After applying these selection criteria, a total of 55 citrate wasters were identified and randomly matched 1:3 by age and sex to other stone formers for a final comparative cohort of n = 165. Univariate analyses with chi-square and t-tests were used to assess differences in demographic, clinical, stone and 24-hour urine characteristics.
Results: Citrate wasters had significantly higher mean ± SD BMI (35.0 ± 7.3 vs 29.9 ± 7.9 kg/m2, p < 0.001) and a higher prevalence of diabetics (61.8 vs 20.6%, p < 0.001). Calcium oxalate monohydrate (COM) and uric acid stones were the two most common stones the citrate wasting group (70% and 15% respectively), while COM and hydroxyapatite stones were most common in the control group (58% and 20% respectively). Uric acid stones were more commonly observed among citrate wasters (15% vs 7%, p = 0.096). On 24-hour urine analysis, the citrate wasting group showed higher urine values of calcium, oxalate, uric acid, and sodium (all p<0.001; see Figure). Notably, urine pH showed no difference between groups. These results were largely unchanged when examining differences by sex.
Conclusions: Nephrolithiasis patients who excrete > 1500mg of urinary citrate per day are more likely to be obese and diabetic, with generally worse urinary analytes overall relating to stone recurrence risk. Further investigation is needed on the etiologic and clinical implications of these findings. Source of