Beta-2-microglobulin is superior to N-acetyl-beta-glucosaminidase in predicting prognosis in idiopathic membranous nephropathy.

BACKGROUND: An accurate prediction of prognosis in patients with idiopathic membranous nephropathy (iMN) would allow restriction of immunosuppressive treatment to patients who are at highest risk for end-stage renal disease (ESRD). Several markers of proximal tubular cell injury have been used as predictors of prognosis. In this study we compared the accuracy of urinary beta-2-microglobulin (U beta 2m) and N-acetyl-beta-glucosaminidase (U beta-NAG) in predicting renal insufficiency and remission rates. METHODS: Fifty-seven patients with iMN (38 M, 19 F; age 48 +/- 16 years), a nephrotic syndrome and a serum creatinine level <135 micromol/l were studied prospectively. At baseline, a standardised measurement was carried out to determine renal function and protein excretion. The end-point renal failure was defined as a serum creatinine exceeding 135 micromol/l or an increase in serum creatinine by >50%. Remission was defined as a proteinuria <2.0 g/day with stable renal function. RESULTS: The mean follow-up was 80 +/- 36 months. The mean serum creatinine concentration was 89 +/- 20 micromol/l, serum albumin 24 +/- 5.3 g/l and proteinuria 8.9 +/- 4.8 g/24 h. Thus far, 28 (49%) patients have reached the predefined end point of renal failure. Multivariate analysis identified U beta 2m as the strongest independent predictor for the development of renal insufficiency. Sensitivity and specificity were 81 and 90% respectively for U beta 2m (threshold value 54 microg/mmol cr), and 74 and 81% respectively for U beta-NAG (threshold value 2.64 U/mmol cr). The overall remission rate was 44%. A remission occurred in 78% of patients with low U beta 2m and in 14% of patients with high U beta 2m, and respectively in 71% of patients with low U beta-NAG and 21% of patients with high U beta-NAG. CONCLUSIONS: Although both U beta 2m and U beta-NAG predicted progression and remission in iMN, U beta 2m was more accurate. High specificity in predicting prognosis should be pursued to avoid unnecessary immunosuppressive therapy. We therefore conclude that U beta 2m is superior to U beta-NAG in predicting prognosis in patients with iMN.