26th February 2025

Investigations in antiphospholipid syndrome

Routine blood tests will usually be normal in primary APLS; however, a prolonged APTT can be seen. Additionally, thrombocytopenia can be seen in around 30% of patients, particularly around the time of a thrombotic event.

Diagnosis of APLS requires at least one of the antiphospholipid antibodies to be positive on two occasions within 5 years of the thrombotic event. These are anti-2 glycoprotein-1 antibodies, anti-cardiolipin antibodies and lupus anticoagulant. Those with more than one positive antibody have a higher risk for thrombotic events.

Patients can have false positive syphilis results, as non-treponemal tests such as VDRL use cardiolipin antigens.