title: Antiprothrombin antibodies: a comparative analysis of homemade and commercial methods. A collaborative study by the Forum Interdisciplinare per la Ricerca nelle Malattie Autoimmuni (FIRMA).
abstract: OBJECTIVE
  Prothrombin (PT) is a target for antibodies with lupus anticoagulant (LA) activity, suggesting the possible application of anti-prothrombin antibody (aPT) assays in patients with antiphospholipid syndrome (APS). Different methods - both homemade and commercial - for the detection of aPT are available, but they seem to produce conflicting results. The purpose of this study was to compare the performance of different assays on a set of well-characterized serum samples.
  
  
  METHODS
  Sera were gathered from 4 FIRMA institutions, and distributed to 15 participating centres. Forty-five samples were from patients positive for LA and/or anticardiolipin antibodies (aCL) with or without APS, and 15 were from rheumatoid arthritis (RA) patients negative for antiphospholipid antibodies. The samples were evaluated for IgG and IgM antibodies using a homemade direct aPT assay (method 1), a homemade phosphatidylserine-dependent aPT assay (aPS/PT, method 2), and two different commercial kits (methods 3 and 4). In addition, a commercial kit for the detection of IgG-A-M aPT (method 5) was used.
  
  
  RESULTS
  Inter-laboratory results for the 5 methods were not always comparable when different methods were used. Good inter-assay concordance was found for IgG antibodies evaluated using methods 1, 3, and 4 (Cohen k > 0.4), while the IgM results were discordant between assays. In patients with thrombosis and pregnancy losses, method 5 performed better than the others.
  
  
  CONCLUSIONS
  While aPT and aPS/PT assays could be of interest from a clinical perspective, their routine performance cannot yet be recommended because of problems connected with the reproducibility and interpretation of the results.
authors.affiliation: Reumatologia e Immunologia Clinica, Ospedale Civile e Università di Brescia, Italy. Tincani@bresciareumatologia.it
authors.forename: A
authors.initials: A
authors.lastname: Tincani
authors.forename: G
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authors.lastname: Morozzi
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authors.lastname: Afeltra
authors.forename: C
authors.initials: C
authors.lastname: Alessandri
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authors.initials: F
authors.lastname: Allegri
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authors.lastname: Bistoni
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authors.lastname: Bizzaro
authors.forename: D
authors.initials: D
authors.lastname: Caccavo
authors.forename: M
authors.initials: M
authors.lastname: Galeazzi
authors.forename: R
authors.initials: R
authors.lastname: Gerli
authors.forename: L
authors.initials: L
authors.lastname: Giovannelli
authors.forename: G
authors.initials: G
authors.lastname: Longobardo
authors.forename: M
authors.initials: M
authors.lastname: Lotzniker
authors.forename: F
authors.initials: F
authors.lastname: Malacarne
authors.forename: P
authors.initials: P
authors.lastname: Migliorini
authors.forename: A
authors.initials: A
authors.lastname: Parodi
authors.forename: F
authors.initials: F
authors.lastname: Pregnolato
authors.forename: A
authors.initials: A
authors.lastname: Radice
authors.forename: V
authors.initials: V
authors.lastname: Riccieri
authors.forename: M
authors.initials: M
authors.lastname: Ruffelli
authors.forename: R A
authors.initials: RA
authors.lastname: Sinico
authors.forename: R
authors.initials: R
authors.lastname: Tozzoli
authors.forename: D
authors.initials: D
authors.lastname: Villalta
authors.forename: R
authors.initials: R
authors.lastname: Marcolongo
authors.forename: P
authors.initials: P
authors.lastname: Meroni
mesh_terms: D000888:Antibodies, Anti-Idiotypic / Q000097:blood*; D016736:Antiphospholipid Syndrome / Q000097:blood / Q000276:immunology*; D001172:Arthritis, Rheumatoid / Q000097:blood / Q000276:immunology*; D004797:Enzyme-Linked Immunosorbent Assay / Q000379:methods*; D005260:Female; D006801:Humans; D007074:Immunoglobulin G / Q000097:blood; D007075:Immunoglobulin M / Q000097:blood; D016682:Lupus Coagulation Inhibitor / Q000276:immunology; D011516:Prothrombin / Q000276:immunology*; D015203:Reproducibility of Results
chemical_list: D000888:Antibodies, Anti-Idiotypic; D007074:Immunoglobulin G; D007075:Immunoglobulin M; D016682:Lupus Coagulation Inhibitor; D011516:Prothrombin