Which tests are most useful to evaluate suspected antiphospholipid syndrome?

• A. Lupus anticoagulant testing (dRVVT), anticardiolipin antibodies, and anti-beta2-glycoprotein I antibodies, repeated weeks apart
• B. PT and INR only
• C. Platelet function tests
• D. Bleeding time

Answer: (A)

Evaluating suspected antiphospholipid syndrome relies on detecting persistent antiphospholipid antibodies and recognizing associated clinical events. The best approach is to test for lupus anticoagulant (using a LA-sensitive assay like the diluted Russell viper venom test, dRVVT), along with antibodies against cardiolipin and against beta2-glycoprotein I, and to repeat these tests weeks apart to confirm persistence.

Lupus anticoagulant testing targets a functional effect of these antibodies on phospholipid-dependent coagulation tests, which helps identify the prothrombotic antibody present in APS. Anticardiolipin and anti-beta2-glycoprotein I antibodies are detected by immunoassays and provide complementary antibody identification. Repeating the tests ensures the antibodies are persistent rather than transient, such as those that can appear briefly during infections. Together, this trio of tests acquired on two occasions separated by time aligns with diagnostic criteria for APS.

The other options don’t fit because PT/INR are general coagulation measures and don’t specifically detect antiphospholipid antibodies; platelet function tests and bleeding time assess platelet function or bleeding risk rather than APS antibody status.