The Cardiolipin Antibody (ACL) - IgM Test is a diagnostic blood test used to detect and measure the levels of IgM class antibodies directed against cardiolipin, a crucial phospholipid found in cell membranes. This test is a key component in the evaluation of Antiphospholipid Syndrome (APS), an autoimmune disorder associated with an increased risk of blood clots (thrombosis) in arteries and veins, as well as pregnancy complications like recurrent miscarriages. While IgG antibodies are more commonly associated with APS, testing for IgM provides additional diagnostic sensitivity, especially in acute phases of the condition. The result helps clinicians assess a patient’s risk profile.