Objective
To assess the value of a combination of anti–β2‐glycoprotein I (anti‐β2GPI) domain I antibody and anti–phosphatidylserine/prothrombin complex (anti‐PS/PT) antibody tests for the diagnosis of antiphospholipid syndrome (APS).
Methods
This cross‐sectional study involved a cohort of the patients who visited our clinic from April 2005 to March 2013. Tests for anti‐β2GPI domain I antibodies, IgG anti‐PS/PT antibodies, and IgM anti‐PS/PT antibodies, together with tests for criteria‐defined antiphospholipid antibodies (aPL), were performed in all patients. The total antiphospholipid score (aPL‐S) was calculated for each patient according to titers of and positivity for aPL.
Results
The study enrolled 157 patients (51 patients with APS and 106 with non‐APS autoimmune diseases). All 21 patients positive for both anti‐β2GPI domain I antibodies and IgG and/or IgM (IgG/IgM) anti‐PS/PT antibodies had APS with a high total aPL‐S (median 46, range 26–76), as did all of the 10 patients who were positive for anti‐β2GPI domain I antibodies but negative for IgG/IgM anti‐PS/PT antibodies (median 22, range 4–39). Of the 14 patients who were positive for IgG/IgM anti‐PS/PT antibodies but negative for anti‐β2GPI domain I antibodies, 11 (79%) had APS; these individuals also had high total aPL‐S values (median 23, range 11–60). In contrast, only 9 of the 112 patients (8%) with none of these antibodies had APS.
Conclusion
The combination of the IgG anti–β2GPI domain I antibody and IgG/IgM anti‐PS/PT antibody tests shows a high positive predictive value for the diagnosis of APS and a strong correlation with the aPL‐S. This combination as the first‐line test for aPL may contribute to the simple and definite identification of APS with a high risk of thrombosis in clinical practice.