title: C4d as a diagnostic tool in membranous nephropathy.
abstract: BACKGROUND
  membranous nephropathy (MN) is the most common cause of nephrotic syndrome in adults. The diagnosis is based on typical findings observed using electron microscope (EM) and immunofluorescence (IF) studies. On some occasions, tissues are only available for analysis using an optical microscope (OM); in these cases, it can be difficult to differentiate between MN and minimal change disease (MCD). Recently, the use of C4d immunohistochemical staining has spread. Very little information is available regarding C4d deposits in MN. Our study consisted of analysing whether C4d staining of samples embedded in paraffin could be useful for diagnosing MN.
  
  
  METHODS
  Ours was a retrospective study including all patients diagnosed with MN by renal biopsy in our unit between January 2001 and October 2008. We only included adult patients with a definitive diagnosis of MN or idiopathic MCD by OM, IF, and ME studies. In October 2008, 3µm sections of renal tissue fixed in formaldehyde were removed from paraffin and rehydrated. The samples were then stained for C4d immunohistochemical analysis using anti-human polyclonal antibodies obtained from rabbits.
  
  
  RESULTS
  Our study included a final sample of 19 patients with MCD and 21 with MN. No C4d deposits were observed in any of the glomeruli in patients with MCD, and 100% of these patients were classified as negative. However, C4d deposits were detected in 100% of patients with MN, and were observable in all glomeruli with a uniform granular distribution, demarcating all capillary loops.
  
  
  CONCLUSIONS
  C4d immunohistochemical staining is a very useful tool for diagnosing MN.
authors.affiliation: Hospital Universitario Reina Sofía, Córdoba, Spain. espinosahe@ono.com
authors.forename: Mario
authors.initials: M
authors.lastname: Espinosa-Hernández
authors.forename: Rosa
authors.initials: R
authors.lastname: Ortega-Salas
authors.forename: María
authors.initials: M
authors.lastname: López-Andreu
authors.forename: José M
authors.initials: JM
authors.lastname: Gómez-Carrasco
authors.forename: M José
authors.initials: MJ
authors.lastname: Pérez-Sáez
authors.forename: Carlos
authors.initials: C
authors.lastname: Pérez-Seoane
authors.forename: Pedro
authors.initials: P
authors.lastname: Aljama-García
mesh_terms: D000293:Adolescent; D000328:Adult; D000818:Animals; D000911:Antibodies, Monoclonal / Q000276:immunology; D015415:Biomarkers / Q000032:analysis; D001706:Biopsy; D015935:Complement C4b / Q000032:analysis* / Q000276:immunology; D003937:Diagnosis, Differential; D005260:Female; D015433:Glomerulonephritis, Membranous / Q000175:diagnosis* / Q000378:metabolism / Q000473:pathology; D006801:Humans; D007124:Immunoenzyme Techniques; D007074:Immunoglobulin G / Q000276:immunology; D007678:Kidney Glomerulus / Q000737:chemistry / Q000648:ultrastructure; D008297:Male; D008854:Microscopy, Electron; D008856:Microscopy, Fluorescence; D008875:Middle Aged; D009402:Nephrosis, Lipoid / Q000175:diagnosis; D016612:Paraffin Embedding; D010446:Peptide Fragments / Q000032:analysis* / Q000276:immunology; D011817:Rabbits; D012189:Retrospective Studies; D013194:Staining and Labeling / Q000379:methods; D055815:Young Adult
chemical_list: D000911:Antibodies, Monoclonal; D015415:Biomarkers; D007074:Immunoglobulin G; D010446:Peptide Fragments; D015935:Complement C4b; C032261:complement C4d