How is antiphospholipid syndrome diagnosed?
People who have had thrombotic problems, miscarriages, or low platelet counts should be tested for antiphospholipid antibodies. Blood tests that measure for blood clotting are used to test for this antibody. The activated partial thromboplastin time (aPTT) is a widely available blood clotting test that is often used. If the aPTT is normal, more sensitive blood clotting tests should be done. If the number of seconds that it takes the blood to clot is prolonged, the physician will suspect that lupus anticoagulant is present.
The presence of Anticardiolipin antibody (IgG, IgM, and IgA) and anti-β2 glycoprotein I may also indicate an APS diagnosis. The presence of IgG and IgA as well as anti-β2 glycoprotein are most often associated with blood clotting. Some lupus patients with very high IgM levels have a problem called "hemolytic anemia," in which their immune system attacks their red blood cells.
There are no current recommendations on the timing of repeat tests for these antibodies.
Michelle Petri, MD, MPH
Dr. Petri is the Director of the Hopkins Lupus Cohort, a longitudinal study of morbidity and mortality in systemic lupus erythematosus, and Co-Director of the Hopkins Lupus Pregnancy Center. Read Bio