Reappraisal of serum beta2-microglobulin as marker of GFR.

Introduction: Beta 2 microglobulin (beta2M) 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 beta2M as markers of GFR.
Patients and Methods: In 160 adult patients, with various kidney diseases and different GFR, serum Cr (autoanalyzer), serum beta2M (RIA) and GFR (bladder cumulative method using 99mTc-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=3.112-0.716 lnGFR; r=0.92) and ln serum beta2M (lnbeta2M= 4.274-0.814 lnGFR; r = 0.90). With decreasing GFR the increase in serum beta2M 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 beta2M to a GFR 65.0. With decreasing GFR the increase of serum beta2M occurs before than that of serum Cr.
Conclusions: With declining renal function, serum beta2M increases more and before than serum Cr. Serum beta2M is a good endogenous marker of GFR, better than serum Cr.