Antiphospholipid Antibodies, IgM

The Antiphospholipid Antibodies, IgM test (also referred to as IgM aPL or APA IgM) supports the workup of suspected antiphospholipid syndrome by identifying the IgM isotype of antiphospholipid antibodies. It is ordered in patients with arterial or venous thrombosis, recurrent pregnancy loss—especially during the second or third trimester—unexplained thrombocytopenia, prolonged activated partial thromboplastin time, or clinical features concerning for thrombotic microangiopathy. When combined with clinical criteria and repeat testing to document persistence (≥6 weeks), results inform diagnostic classification and risk assessment.

Antiphospholipid antibodies target phospholipids and the proteins that bind them within cellular membranes and on platelets. Their presence is associated with a prothrombotic state affecting both arterial and venous circulations and with obstetric complications, including recurrent fetal loss and preeclampsia. These antibodies are a feature of antiphospholipid syndrome, which is defined by thrombotic events, pregnancy morbidity, and thrombocytopenia. The syndrome may occur as a primary condition or secondary to other autoimmune diseases, most commonly systemic lupus erythematosus. Detection of aPL, including the IgM isotype, is not sufficient for diagnosis; clinical classification requires compatible clinical criteria and demonstration that antibodies persist on repeat testing.