The Anti-Cardiolipin Antibody IgG test measures the presence of IgG antibodies against cardiolipin, a fat molecule found in cell membranes. Elevated levels of these antibodies can indicate antiphospholipid syndrome (APS), a disorder that increases the risk of blood clots, recurrent miscarriages, and other complications. This test is used to help diagnose APS, particularly in patients with a history of unexplained blood clots or pregnancy-related issues. A blood sample is required for this test.