An accurate prediction of the prognosis of patients with
idiopathic membranous nephropathy (iMN) should allow restriction of immunosuppressive treatment to patients who are at highest risk for
ESRD. On the basis of retrospective studies, it has previously been suggested that the urinary excretions of beta2-microglobulin (Ubeta2m) and
IgG (UIgG) are useful predictors of
renal insufficiency in patients with iMN. The threshold values of 0.5 micro/min (Ubeta2m) and 250 mg/24 h (UIgG) have been validated in a new and larger patient cohort. From 1995 onward, 57 patients with iMN (38 men, 19 women; age 48 +/- 16 yr), a
nephrotic syndrome, and a serum
creatinine level </=1.5 mg/dl were studied prospectively. At baseline, a standardized measurement was carried out to determine renal function and
protein excretion. The end point renal death was defined as a serum
creatinine exceeding 1.5 mg/dl or a rise of serum
creatinine of >50%. Mean (+/-SD) follow-up was 53 +/- 23 mo. Thus far, 25 (44%) of the patients have reached the end point renal death. Multivariate analysis confirmed Ubeta2m as the strongest independent predictor for the development of
renal insufficiency. Sensitivity and specificity were 88 and 91%, respectively, for Ubeta2m, and both were 88% for UIgG. When the excretions of both
proteins were combined, specificity improved to 97%. It is concluded that the present data validate the accuracy of Ubeta2m and of UIgG in predicting renal outcome in patients with iMN. These markers can be used to guide decisions on the start of immunosuppressive treatment.