Is hyperuricosuria really a risk factor for calcium oxalate stone formation?

Abstract

In the seventies of the last century the term hyperuricosuric calcium oxalate (CaOx) urolithiasis has been coined. Allopurinol significantly decreased the recurrence in CaOx stone formers. Nevertheless, the role of hyperuricosuria has been questioned. Other mechanisms could have decreased the risk for recurrence. The underlying mechanisms are not clear. All these studies have been performed with only a limited number of patients. We studied n=2,480 consecutive patients with CaOx stones. For stone analysis, x-ray diffraction was used. The following parameters were examined in all patients: age, sex, body mass index (BMI), arterial blood pressure, stone episodes, diabetes mellitus; blood: creatinine, glucose, uric acid, calcium, sodium and potassium; urine: pH, volume, calcium, uric acid, citrate, ammonia and urea. According to the uric acid excretion (UAE), patients were divided into two groups: 1. UAE > 4 mmol/d (hyperuricosuria), 2. UAE ≤ 4 mmol/d (normouricosuria). We observed significant correlations between UAE and sex, age, BMI, blood pressure, serum values of creatinine, sodium, urine volume, urine levels of calcium, citrate, urea and ammonia as well as serum calcium. No significant correlations were seen to the stone frequency (number of stone episodes), serum potassium and urine pH. In group 1 (n=741), there were 87.2% male and 12.8% female patients; in group 2 (n=1,739), the ratio was 60.6:39.4%. In the hyperuricosuric group, there were significantly more males than in the normouricosuric collective. Hyperuricosuric subjects had a higher BMI, higher blood levels of uric acid and glucose, a higher diuresis, a higher excretion of calcium, urea and ammonium, but a lower excretion of citrate than normouricosuric patients. All the other parameters did not show any significant differences. Especially the number of stone episodes was not different. We concluded that hyperuricosuria went along with many other risk factors for CaOx stone formation, but was not associated with an increased risk for recurrence. Therefore, UAE is not a prognostic marker in CaOx urolithiasis. It is unlikely that hyperuricosuria is a real risk factor for CaOx stone formation and hyperuricosuric CaOx urolithiasis is an own entity.