Determination of clinically significant tests for antiphospholipid antibodies and cutoff levels for obstetric antiphospholipid syndrome

Objective The objective of this paper is to determine which kinds of assays for antiphospholipid antibodies (aPL) should be tested for clinical practice for patients with recurrent pregnancy loss (RPL). Materials and methods We studied 560 patients with a history of RPL prospectively. We determined the obstetric significance of 11 commercially available tested assays for lupus anticoagulant (LA)-aPTT StaClot, phosphatidylserine-dependent antiprothrombin (aPS/PT) IgG, IgM, classical cardiolipin (CL) IgG, IgM, CL IgG, IgM, IgA, and 2glycoprotein I (2GPI) IgG, IgM, IgA Phadia. Obstetric significance was defined as the potential for anticoagulant therapy to improve the subsequent live birth rate, or a difference in the live birth rate between positive and negative untreated cases. Results The LA-aPTT StaClot assay and aPS/PT IgG assay, but not CL IgG, were found to have obstetric significance. Our conventional tests covered positive cases with the aPS/PT IgM and classical CL IgG assays. The results of the LA-aPTT StaClot, LA-aPTT and LA-RVVT assays showed different distributions, although strong or moderate correlation was observed. Conclusion LA-aPTT StaClot and aPS/PT IgG might be suitable for use in routine practice for patients with RPL. Each test for aPL should be ascertained for obstetric significance, because similar assays may have different outcomes.