NDT Advance Access published online on February 28, 2008
Nephrology Dialysis Transplantation, doi:10.1093/ndt/gfn007
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Beta-2-microglobulin is superior to N-acetyl-beta-glucosaminidase in predicting prognosis in idiopathic membranous nephropathy
1 Department of Nephrology, Radboud University Nijmegen Medical Center, Nijmegen, The Netherlands 2 Department of Clinical Chemistry, Radboud University Nijmegen Medical Center, Nijmegen, The Netherlands
Correspondence and offprint requests to: Julia M. Hofstra, Department of Nephrology 464, Radboud University Nijmegen Medical Center, PO Box 9101, 6500 HB Nijmegen, The Netherlands. Tel: +31-24-3614761; Fax: +31-24-3540022; E-mail: J.Hofstra{at}nier.umcn.nl
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Abstract |
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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 (Uβ2m) and N-acetyl-beta-glucosaminidase (Uβ-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 µmol/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 µmol/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 µmol/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 Uβ2m as the strongest independent predictor for the development of renal insufficiency. Sensitivity and specificity were 81 and 90% respectively for Uβ2m (threshold value 54 µg/mmol cr), and 74 and 81% respectively for Uβ-NAG (threshold value 2.64 U/mmol cr). The overall remission rate was 44%. A remission occurred in 78% of patients with low Uβ2m and in 14% of patients with high Uβ2m, and respectively in 71% of patients with low Uβ-NAG and 21% of patients with high Uβ-NAG.
Conclusions: Although both Uβ2m and Uβ-NAG predicted progression and remission in iMN, Uβ2m was more accurate. High specificity in predicting prognosis should be pursued to avoid unnecessary immunosuppressive therapy. We therefore conclude that Uβ2m is superior to Uβ-NAG in predicting prognosis in patients with iMN.
Keywords: beta-2-microglobulin; membranous nephropathy; N-acetyl-beta-glucosaminidase; prognostic markers; renal outcome
Received for publication: 19.10.07
Accepted in revised form: 3. 1.08
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