[Dynamics of uric acid metabolism in hyperuricemia]

This paper is a review of the studies on urate metabolism of gouty patients with hyperuricemia and normal healthy subjects, performed mainly in our laboratory. The pathogenesis of hyperuricemia consisted of overproduction and underexcretion, which can be estimated using the urate clearance test. Overproduction was defined as urinary urate excretion (Uua) higher than [0.030 Cua + 0.325] mg/kg/hr and underexcretion as urate clearance (Cua) lower than 6.1 ml/min. According to those criteria, hyperuricemia was classified into the 4 types of overproduction (12%), underexcretion (60%), combined (25%) and normal type (3%). Patients with overproduction had a tendency of lower serum urate level (Sua) than those with underexcretion, higher Uua than those with the normal control and lower Cua and creatinine clearance (Ccr) than those with the normal control. Patients with underexcretion had a tendency of higher Sua and lower Cua, Ccr and Cua/Ccr ratio than those with overproduction or normal control. Patients with the combined type had the highest Sua among the 4 types, and those with the normal type had the lowest Sua. These findings indicate that each subtype of hyperuricemia has characteristic features in the urate metabolism, which are valuable for better understanding and treatment of hyperuricemia in gouty patients.