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Antiprothrombin antibodies: a comparative analysis of homemade and commercial methods. A collaborative study by the Forum Interdisciplinare per la Ricerca nelle Malattie Autoimmuni (FIRMA)
A. Tincani, G. Morozzi, A. Afeltra, C. Alessandri, F. Allegri, O. Bistoni, N. Bizzaro, D. Caccavo, M. Galeazzi, R. Gerli, L. Giovannelli, G. Longobardo, M. Lotzniker, F. Malacarne, P. Migliorini, A. Parodi, F. Pregnolato, A. Radice, V. Riccieri
CER2995
2007 Vol.25, N°2
PI 0268, PF 0274
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PMID: 17543152 [PubMed]
Abstract
OBJECTIVES:
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.PATIENTS AND
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.
