Studies on circadian periodicity of serum and urinary urate in healthy Indians and renal stone formers.

The circadian patterns of serum and urinary urate were studied in 25 healthy Indians and 25 renal stone formers. A marked circadian variation in uric acid concentration was recorded in both the groups with acrophases at 1441 and 1347 hr, respectively (cosinor analysis). Similarly, cosinor rhythmometry confirmed a significant circadian rhythm in urinary uric acid levels during different hours of the 24-hr day-night period in healthy Indians (acrophase at 1229 hr) and renal stone formers (acrophase at 1121 hr). Serum uric acid was found to be elevated at all time points during the 24-hr period in the stone formers compared to healthy subjects. The excretory pattern, however, did not exhibit any significant difference in uric acid levels between the two groups although the excretion was a little higher in the stone formers compared to the healthy controls. Maximum urate excretion at 1121 hr (around midday) might be the peak hour for maximum crystallization of stones containing an admixture of urate in stone formers; if such is true, it could prove to be of clinical significance when trying to inhibit crystallization of renal stones and to minimize the risk of crystal growth (urate admixture) in renal tubules.