print   Print full article


The aims of testing are to diagnose APS and to distinguish it from other causes of symptoms and complications. Not everyone who has antiphospholipid antibodies has symptoms or complications. Therefore, a diagnosis of APS is made based upon both clinical signs and the presence of autoantibodies. At least one clinical sign and one autoantibody must be present. The following consensus guidelines are used:

Revised Classification Criteria for the Antiphospholipid Antibody Syndrome*

Clinical criteria

Laboratory criteria

Vascular thrombosis:

  • One or more confirmed clinical episodes of arterial, venous, or small-vessel blood clot occurring in any tissue or organ

Pregnancy complications: 

  • One or more unexplained deaths of a physically normal fetus at or after the 10th week of pregnancy
  • One or more premature births of a physically normal newborn at or before the 34th week of pregnancy due to pre-eclampsiaeclampsia, or a placenta that does not function properly
  • Three or more unexplained consecutive miscarriages before the 10th week of pregnancy

Positive test for one of the autoantibodies must be present on two or more occasions at least 12 weeks apart:

  • Lupus anticoagulant: present according to the guidelines of the International Society on Thrombosis and Hemostasis
  • Anticardiolipin antibody present at a medium or high level
  • Anti-β2GP1antibody: present at a high level, greater than the 99th percentile for normal (as established by the testing laboratory)

*Established in 2006 by the 11th International Congress on Antiphospholipid Antibodies

Laboratory Tests

Blood tests that are used to detect the presence of autoantibodies include:

Other tests that may be ordered include:

  • Activated partial thromboplastin time (APTT, to evaluate blood clotting)
  • Full blood count (FBC, to evaluate blood cells and platelets)
  • A variety of additional tests to evaluate other causes for a person's symptoms, such as 1:1 Mix study (dilute APTT) to detect lupus anticoagulant activity

Non-Laboratory Tests

Imaging scans may be performed to confirm a thrombotic episode, to locate a blood clot, evaluate organ damage, and to monitor a fetus. These may include:

  • CT scan
  • MRI
  • Ultrasounds to detect blood clots and to monitor fetal health and growth
  • Echocardiograph to detect heart valve abnormalities that can occur with APS

For more on these, see the web sites Inside Radiology (Australia) and (US).

Last Review Date: June 14, 2019