INTERLABORATORY VARIATION IN ANTIPHOSPHOLIPID ANTIBODY TESTING

OBJECTIVE: Because of the widespread use of antiphospholipid antibody testing in the evaluation of patients with recurrent pregnancy loss, we evaluated the consistency of results among laboratories testing for anticardiolipin antibody and the lupus anticoagulant. STUDY DESIGN: A questionnaire regarding methods used and samples of blood from 20 patients were sent to five university-based and five commercial facilities for antiphospholipid antibody testing. RESULTS: The responses of the participating laboratories to the questionnaires revealed significant differences in methods, standardization, and units of reporting. For anticardiolipin antibody, the number of specimens found to be positive for any isotype (immunoglobulin G, M, or A) varied considerably among laboratories, with a range of 5 to 13. All laboratories were in agreement (i.e., at least one isotype was present or all were absent) for only 5 of 20 specimens (25%). In contrast, lupus anticoagulant results were more reproducible, although one facility reported results markedly discordant from the other four laboratories. CONCLUSION: These observations suggest that significant interlaboratory variation exists in antiphospholipid antibody, and particularly anticardiolipin antibody, testing and might lead to unnecessary therapeutic interventions.