Variability of anti-β2 glycoprotein I antibodies measurement by commercial assays

Guido Reber; Angela Tincani; Marielle Sanmarco; Philippe de Moerloose; Marie-Claire Boffa

doi:10.1160/TH05-02-0081

Thrombosis and Haemostasis, Table of Contents

Thromb Haemost 2005; 94(03): 665-672
DOI: 10.1160/TH05-02-0081

New Technologies and Diagnostic Tools

Schattauer GmbH

Variability of anti-β₂ glycoprotein I antibodies measurement by commercial assays

A collaborative study in the frame of the European Forum on Antiphospholipid Antibodies Standardization Group

Guido Reber

¹Division of Angiology and Haemostasis, Geneva University Hospital and Faculty of Medicine, Switzerland

,

Angela Tincani

²Clinical Immunology Unit, Brescia Hospital, Italy

,

Marielle Sanmarco

³Laboratoire d’Immunologie, Hôpital de la Conception, Marseille, France

,

Philippe de Moerloose

¹Division of Angiology and Haemostasis, Geneva University Hospital and Faculty of Medicine, Switzerland

,

Marie-Claire Boffa

⁴Department of Internal Medicine JC Piette, Hôpital de la Pitié, Paris, France

› Author Affiliations

Abstract

Summary

The aim of this study was to evaluate the agreement in assay results between commercial kits for the measurement of anti- β2glycoprotein I antibodies. Ten manufacturers provided one IgG and one IgM kit to three testing centres. Samples from patients with primary (n=13) or secondary (n=3) antiphospholipid syndrome (APS), from lupus patients without APS features (n=6) and from normal individuals (n=2) were tested in the three centres according to manufacturers’ instructions. Dilutions in normal serum of a pool made from positive patients’ samples (Forum Calibrators) and dilutions of humanized monoclonal antibodies (MoAbs) were used as additional calibrators. The calibration curves obtained with each calibrator differed widely between kits. The rate of positivity of patients’ samples varied from 7 to 16 for IgG and from 2 to 17 for IgM, depending on the kit. Perfect agreement occurred in 12/22 samples for IgG and 5/22 samples for IgM. Samples from normals were found negative by all kits. Between kits, cutoff values varied up to five fold when expressed in Forum Calibrators arbitrary units and up to three fold when expressed in MoAbs equivalents. Examination of discrepant samples indicated that about half of the discrepancies, scoring 8:2 and 9:1, involved the same few kits. In highly discrepant samples, some kits appeared as high responders as compared to others. In conclusion, with the exception of a few kits, agreement in assay results was acceptable. In conclusion, additional efforts are however necessary, especially concerning the way to assess the cutoff point and the adoption of a reference calibrator, in order to improve standardization of the assays.

Keywords

Anti-β2glycoprotein I antibodies - assays - standardization - antiphospholipid antibodies

Full Text

References

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