Résumé
Background: Improving harmonization of the clinical interpretation of anticardiolipin (aCL) and anti–β2-glycoprotein I (aβ2GPI) antibodies immunoglobulin G (IgG)/immunoglobulin M (IgM) in the diagnosis of antiphospholipid syndrome (APS) is desirable. Likelihood ratios (LRs) with corresponding test–result intervals can identify the power of a test to discriminate between a diseased and nondiseased patient and may be useful for the semiquantitative interpretation of aCL/aβ2GPI results.Objectives: To determine moderate and high thresholds for aCL and aβ2GPI IgG/IgM measured with chemiluminescent immunoassay, enzyme-linked immunosorbent assay, fluorescence enzyme immunoassay, and multiplex flow immunoassay.Methods: aCL and aβ2GPI antibodies IgG/IgM were determined with 4 solid-phase systems in a case–control study population including 381 APS patients and 727 controls. Interval-specific LRs (IS-LR) were calculated for ranges determined by prespecified specificity and sensitivity levels. Three methods were used for determining thresholds that separated low, moderate, and high positive antibody levels. Interassay agreement was checked with Cohen’s kappa statistics.Results: Assay- and antibody-specific thresholds demonstrated increasing IS-LR, reflecting different clinical significance for low, moderate, and high levels, especially for IgG aCL and aβ2GPI and in thrombotic APS. IS-LRs per antibody and unit range were comparable across solid-phase platforms resulting in enhanced harmonization of result interpretation. Agreement between assays for identifying high levels was improved by semiquantitative interpretation compared with that by quantitative reporting.Conclusion: aCL and aβ2GPI IgG/IgM moderate and high thresholds were determined for 4 analytical platforms. Thresholds improve harmonized interpretation of aCL/aβ2GPI levels across platforms. The proposed thresholds should be verified in an independent case–control study to check interlaboratory transferability.