Low-molecular-weight proteins as prognostic markers in idiopathic membranous nephropathy |
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Authors: | van den Brand Jan A J G Hofstra Julia M Wetzels Jack F M |
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Institution: | Department of Nephrology, Radboud University Nijmegen Medical Centre, Nijmegen, The Netherlands. a.vandenbrand@nier.umcn.nl |
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Abstract: | SummaryBackgroundAccurate prediction of prognosis in idiopathic membranous nephropathy (iMN) allows restriction of immunosuppressive therapy to patients at high risk for ESRD. Here we re-evaluate urinary low-molecular-weight proteins as prognostic markers and explore causes of misclassification.Design, setting, participants, & measurementsIn a cohort of 129 patients with serum creatinine concentration <135 μmol/L and proteinuria ≥3.0 g/10 mmol, urinary α1- (uα1m) and β2-microglobulin (uβ2m) excretion rate was determined. Urinary α1m and uβ2m-creatinine ratio was also obtained. We defined progression as a rise in serum creatinine ≥50% or ≥25% and an absolute level ≥135 μmol/L.ResultsMedian survival time was 25 months, and 47% of patients showed progression. The area under the receiver operating characteristic curve for uβ2m was 0.81 (95% CI: 0.73 to 0.89). Using a threshold value of 1.0 μg/min, sensitivity and specificity were 73% and 75%, respectively. Similar accuracy was observed for the uβ2m-creatinine ratio with sensitivity and specificity of 75% and 73%, respectively, at a threshold of 1.0 μg/10 mmol creatinine. Similar accuracy was found for uα1m and uα1m-creatinine ratio. Blood Pressure and cholesterol contributed to misclassification. Repeated measurements improved accuracy in patients with persistent proteinuria: the positive predictive value of uβ2m increased from 72% to 89% and the negative predictive value from 76% to 100%.ConclusionsUrinary excretion of uα2m and uβ2m predict prognosis in iMN. A spot urine sample can be used instead of a timed sample. A repeated measurement after 6 to 12 months increases prognostic accuracy. |
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