Hyperuricosuric Calcium Stoneformers: Effect on Fasting and Calcium Hyperabsorption

We have previously reported that serum urate, urinary urate and the fractional excretion of urate (FEurate) do not differ between male idiopathic Ca stoneformers and normal subjects, following an overnight fast, and a similar non-linear negative correlation exists between FEurate and serum urate levels in these two groups1. This latter observation demonstrates the role of the kidney in altering the distribution of urate between serum and urine. In 24-h non-fasting urine collections, Coe2 has reported a 29% incidence of hyperuricosuria in Ca stoneformers. This value is similar to the 33% incidence we have found in male Ca stoneformers (urine urate > 800 mg/day). Coe and Kavalich3 have suggested that excessive dietary purine may be a major factor contributing to hyperuricosuria in these patients. The present study examines other factors, apart from dietary purine, that may alter urinary urate excretion in idiopathic Ca stoneformers.