Antiphospholipid Syndrome (APS) Profile

Plasma, frozen; and serum, room temperature

Three 2-mL citrated plasma tubes and 2 mL serum

Blue-top (sodium citrate) platelet-free plasma tubes and red-top tube or gel-barrier tube

Ideally, the patient should not be on anticoagulant therapy. Avoid warfarin (Coumadin®) therapy for two weeks prior to the test and heparin, direct Xa, and thrombin inhibitor therapies for about three days prior to testing.

Qualitative detection of lupus anticoagulants (LA) in plasma;⁶ semiquantitative detection of anticardiolipin and β₂-glycoprotein 1 (β2GP1) antibodies in serum

Anticoagulant therapies may result in false-positive LA results but will not interfere with aCL and β₂GP1 testing.

Clot; enzyme-linked immunosorbent assay (ELISA). A written assessment of the APS profile results is also provided as an aid in interpretation.

Antiphospholipid antibodies are a heterogeneous population of immunoglobulins directed against phospholipid-binding proteins that fall into one or two groups: lupus anticoagulants (which are identified using plasma-based clotting assays) and solid phase antibodies (which are identified using enzyme immunoassays and include anticardiolipin antibodies, antibodies to β₂-glycoprotein 1 (β2GP1), antibodies to prothrombin, and others). Antiphospholipid antibodies, if present persistently during at least a 12-week period, may be associated with venous thrombosis, pulmonary embolism, arterial thrombosis, and pregnancy morbidity including recurrent fetal loss.^7,8 In order to determine the presence of APS, both lupus anticoagulants (LA) and immunoassays for anticardiolipin and β2GP1 antibodies should be performed. Lupus anticoagulants are nonspecific inhibitors that extend the clotting time of phospholipid-dependent clotting assays, such as the activated partial thromboplastin time (aPTT).^6,7 Unlike specific factor inhibitors, LA are not associated with an increased bleeding risk, unless the patient also suffers from thrombocytopenia or hypoprothrombinemia as a manifestation of the antibody. LA do not specifically inhibit individual coagulation factors; rather they neutralize anionic phospholipid-protein complexes that are involved in the coagulation process. Prolongation of clot-based assays is highly dependent on the sensitivity of the reagent employed to the presence of LA. Reagents with reduced amounts of phospholipid, such as the hexagonal phospholipid neutralization assay (aPTT LA) and dilute Russell viper venom time (dRVVT), have enhanced sensitivity for LA.⁶ Due to the heterogeneity of LA antibodies, no single assay will identify all cases.⁸ The International Society of Thrombosis and Haemostasis (ISTH) has established criteria for the diagnosis of lupus anticoagulants; there is also an international consensus statement describing criteria for antiphospholipid syndrome diagnosis.^6-8 The laboratory criteria for definitive APS include one or more of the following; positive anticardiolipin IgG or IgM antibody at significant titer (>40 GPL or MPL units), positive β2GP1 IgG or IgM antibody, positive LA, and at least one result must demonstrate persistence of positivity at an interval of at least 12 weeks. Testing for lupus anticoagulant, anticardiolipin and β2GP1, and the antiphospholipid syndrome that is associated with these antibodies is described in more detail in the online coagulation appendices: Lupus Anticoagulants and Antiphospholipid Syndrome.