Prediction of glomerular filtration rate by serum creatinine and beta 2-microglobulin.

The reciprocal of serum creatinine concentration (1/Cr) is often used to predict glomerular filtration rate (GFR). Serum creatinine also varies with age, size, and muscle mass, and so it may inaccurately estimate GFR. The reciprocal of serum beta 2-microglobulin (1/beta 2mu) has been proposed as an alternative estimator of GFR. This study compares 1/Cr and 1/beta 2mu as predictors of GFR as measured by 125I-iothalamate clearance (CIOT) and creatinine clearance (CCr) in 29 subjects with a wide range of age, size and kidney function, and including 12 chronic hemodialysis patients. 1/beta 2mu was a better predictor of CIOT (r=0.90) and CCr (r=0.87) than 1/Cr (r=0.50 and 0.78) was. In fact, in the nondialysis population, 1/beta 2mu predicted CIOT (r=0.86) about as well as CCr predicted CIOT (r=0.87). Beta 2mu was less dependent on body size than Cr and unlike Cr, was not influenced by dialysis and did increase as GFR decreased with age. Beta 2mu can be useful as an alternative clinical estimate of GFR, particularly when Cr is considerably influenced by factors other than renal function.