Session Information
Title: Antiphospholipid Syndrome: Clinical Manifestations and New Biomarkers in Antiphospholipid Syndrome
Session Type: Abstract Submissions (ACR)
Background/Purpose: The presence IgG and/or IgM beta2 glycoprotein I (β2GPI) antibodies are associated with thrombosis and/or pregnancy-related morbidity in antiphospholipid syndrome (APS) and/or systemic lupus erythematosus (SLE). Some reports show that IgA β2GPI antibodies may be of clinical relevance in certain patient groups. There are, however, concerns regarding the diagnostic performance of these assays probably due to lack of international calibration materials amongst other factors. This study was designed to determine isotype-specific prevalence and correlation between four different aβ2GPI immunoassays in two cohorts of patients.
Methods: IgG, IgM, and IgA β2GPI antibodies were determined in 97 pregnant women with positive antiphospholipid (aPL) antibodies (PROMISSE cohort) and 204 SLE patients (‘HOPKINS’ cohort) with 4 commercial kits (Bio-Rad, Corgenix, INOVA, Phadia). Results were expressed in kit-specific arbitrary units (AU) for IgG, IgM, and IgA as well as in the recently established international consensus units (IU) for IgG and IgM isotypes. Isotype-specific prevalence, Kappa and Spearman’s Rho correlation coefficients were calculated using Analyse-it™.
Results:
The positivity rates of the aβ2GPI tests ranged from 1.0-10.2% and 40.6-63.2% (IgG); 3.9-6.3% and 32.3-47.4% (IgM); and 10.7-20.0% and 18.8-85.3% (IgA) in the HOPKINS and PROMISSE cohorts, respectively. The overall agreement between any two assays ranged from 92.2-99.6% (IgG), 95.4-98.8% (IgM) and 77.6-92.2% (IgA) in both cohorts. While the Kappa coefficients (k) showed moderate-to-almost-perfect agreement for IgG and IgM (0.54-0.98), the analysis revealed fair-to-substantial correlations for IgA β2GPI tests (0.24-0.75). Despite differences in the positivity rates and varying agreements, good quantitative Rho Spearman’s correlation was observed for the IgG and IgM in all 4 kits. Rho correlations were significantly improved when results of the IgG and IgM β2GPI determinations were expressed in IU. However, suboptimal correlations were obtained for the IgA β2GPI assays, with better agreement observed between the Phadia and INOVA kits and between the Bio-Rad and Corgenix assays, respectively.
Conclusion: Overall, our study demonstrates good qualitative agreements between these immunoassays for the determination of IgG and IgM antibody isotypes. The use of consensus IU clearly indicates an improvement in the harmonization of the IgG and IgM β2GPI. Further standardization of the IgA β2GPI assays is warranted.
Disclosure:
A. E. Tebo,
None;
R. Willis,
None;
T. Jaskowski,
None;
J. E. Salmon,
Biogen Idec, BMS, J and J, Merck, Quest,
1,
Roche Pharmaceuticals,
2,
Alexion, Regeneron, Movartis, BMS,
5,
Alliance for Lupus Research, RRF, Kunkel Society ,
6;
M. Petri,
None;
W. D. Branch,
UCB,
5;
S. S. Pierangeli,
None.
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ACR Meeting Abstracts - https://acrabstracts.org/abstract/isotype-dependent-performance-of-beta2glycoprotein-i-immunoassays-in-two-diverse-patient-cohorts-implications-for-assay-harmonization-and-standardization/