A proposal for identifying the low renal uric acid clearance phenotype

Investigation of the genetic basis of hyperuricaemia is a subject of intense interest. However, clinical studies commonly include hyperuricaemic patients without distinguishing between 'over-producers' or 'under-excretors' of urate. The statistical power of studies of genetic polymorphisms of genes encoding renal urate transporters is diluted if 'over-producers' of uric acid are included. We propose that lower than normal fractional renal clearance of urate is a better inclusion criterion for these studies. We also propose that a single daytime spot urine sample for calculation of fractional renal clearance of urate should be preferred to calculation from 24-hour urine collections.