title: Low-molecular-weight proteins as prognostic markers in idiopathic membranous nephropathy.
abstract: BACKGROUND
  Accurate 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.
  
  
  METHODS
  In 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.
  
  
  RESULTS
  Median 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%.
  
  
  CONCLUSIONS
  Urinary 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.
authors.affiliation: Department of Nephrology, Radboud University Nijmegen Medical Centre, Nijmegen, The Netherlands. a.vandenbrand@nier.umcn.nl
authors.forename: Jan A J G
authors.initials: JA
authors.lastname: van den Brand
authors.forename: Julia M
authors.initials: JM
authors.lastname: Hofstra
authors.forename: Jack F M
authors.initials: JF
authors.lastname: Wetzels
mesh_terms: D000328:Adult; D000510:Alpha-Globulins / Q000652:urine*; D015415:Biomarkers / Q000652:urine*; D003404:Creatinine / Q000097:blood; D005260:Female; D015433:Glomerulonephritis, Membranous / Q000401:mortality* / Q000652:urine*; D006801:Humans; D008297:Male; D008875:Middle Aged; D008970:Molecular Weight; D011379:Prognosis; D011507:Proteinuria / Q000401:mortality*; D001613:beta 2-Microglobulin / Q000652:urine*
chemical_list: D000510:Alpha-Globulins; D015415:Biomarkers; C016001:alpha-1-microglobulin; D001613:beta 2-Microglobulin; D003404:Creatinine