Reappraisal of serum beta 2-microglobulin as marker of GFR

Introduction. Beta 2 microglobulin (beta 2M) is filtered by the glomeruli and reabsorbed by the proximal tubular cells where it is metabolized. Its plasma concentration increases with decreasing renal function. Aim. To compare serum creatinine (Cr) and serum beta 2M as markers of GFR. Patients and Methods. In 160 adult patients, with various kidney diseases and different GFR serum Cr (autoanalyzer), serum beta 2M (RIA) and GFR (bladder cumulative method using Tc-99m-DTPA as glomerular tracer) were measured in the same day. Results. A linear relationship was observed between In GFR and both In serum Cr (lnCr = 3.112-0.7161 nGFR; r = 0.92) and In serum beta 2M (ln beta 2M = 4.274-0.814lnGFR; r = 0.90). With decreasing GFR the increase in serum betaM was higher than that of serum Cr (see regression coefficients that are significantly different). The normal upper Limit of serum Cr corresponds to a GFR 48.1 mL/min while that of serum beta 2M to a GFR 65.0. With decreasing GFR the increase of serum beta 2M occurs before than that of serum. Cr. Conclusions. With declining renal function, serum beta 2Mincreases more and before than serum Cr. Serum, beta 2M is a good endogenous marker of GFR, better than serum Cr.