Criteria for diagnosis of antiphospholipid syndrome

Note: Antiphospholipid syndrome is not diagnosed on a positive antiphospholipid-antibody assay alone.

Antiphospholipid syndrome is not diagnosed on a positive antiphospholipid (aPL)-antibody assay alone. Diagnosis of antiphospholipid syndrome requires:

  • at least one clinical manifestation (of thrombotic or obstetric antiphospholipid syndromes) AND
  • positive aPL-antibody markers on 2 occasions at least 12 weeks apart (ie ‘persistent’ aPL antibodies).

The 2023 American College of Rheumatology (ACR) and European League Against Rheumatism (EULAR) Antiphospholipid Syndrome Classification Criteria, developed for research purposes, offers a detailed, weighted scoring system with high specificity for the diagnosis of antiphospholipid syndromeBarbhaiya 2023.

For thrombotic antiphospholipid syndrome, the significant clinical criteria include:

  • arterial thromboembolism, especially stroke or acute myocardial infarction in people under 50 years
  • venous thromboembolism, especially unprovoked deep vein thrombosis and pulmonary embolism
  • microvascular features, such as vasculopathy, nephropathy, pulmonary haemorrhage
  • cardiac valve thickening and regurgitation
  • thrombocytopenia.

For obstetric antiphospholipid syndrome, the significant clinical criteria include:

  • 3 or more early miscarriages (at less than 10 weeks’ gestation)
  • 1 or more fetal loss at or beyond 10 weeks’ gestation
  • late-pregnancy complications, such as premature delivery (before 34 weeks’ gestation) due to severe pre-eclampsia, eclampsia, or placental insufficiency; unexplained fetal death.

There may be some crossover of these 2 main phenotypes, depending on the person’s aPL-antibody profile. It is important to identify people who meet the criteria for thrombotic antiphospholipid syndrome because they require lifelong anticoagulation with warfarin. A direct-acting oral anticoagulant (DOAC) is not appropriate for the majority of peopleTektonidou, 2019Williams, 2022.

Note: People who have thrombotic antiphospholipid syndrome require lifelong anticoagulation with warfarin. A direct-acting oral anticoagulant (DOAC) is not appropriate for the majority of people.