The Anti-Phospholipid Screen IgM test measures the levels of IgM antibodies against several phospholipids, including cardiolipin, phosphatidylinositol, phosphatidylserine, phosphatidic acid, and cofactor beta-2-glycoprotein in human serum or plasma. This test is a valuable diagnostic tool for detecting primary and secondary antiphospholipid syndrome, a condition that increases the risk of blood clots and related complications.