Anti-phosphatidylserine/prothrombin (PS/PT) is a recent advancement in assessing a patient’s risk of thrombosis and pregnancy loss associated with APS. In addition, PS/PT has been found to correlate with lupus anticoagulant (LAC) positivity better than other aPL methods regardless of anticoagulant treatment.

Antibodies to cardiolipin are present in SLE patients (30-40%) and APS. Prevalence of anticardiolipin in APS is high but specificity for APS is lower than other anti-phospholipid antibodies. IgA antibodies to cardiolipin are less prevalent than IgG or IgM but can occur in isolation. Positive results should be confirmed after 12 weeks.

Antibodies to Beta 2 glycoprotein 1 (β2-GP1) show higher specificity than anti-cardiolipin assays. In 3-10% of APS patients, β2-GP1 antibody may be the only positive test. IgA antibodies to β2-GP1 are less prevalent than IgG or IgM but can occur in isolation. Positive results should be confirmed after 12 weeks.

Repeating positive tests:

Guidelines recommend re-testing any positive tests after at least 12 weeks to gain confidence in persistent elevated levels.