**Anti-cardiolipin (aCL) IgG and IgM antibodies** are autoantibodies—immune proteins that mistakenly target the body's own cell membranes, specifically phospholipids.
Testing for both types is essential when evaluating unexplained blood clots, recurrent miscarriages, or autoimmune diseases like systemic lupus erythematosus (SLE). **IgM** antibodies usually appear first during an initial immune response, while **IgG** antibodies develop later and typically persist longer, often carrying a stronger clinical association with clotting risks.
Elevated levels of either antibody serve as primary diagnostic markers for **Antiphospholipid Syndrome (APS)**, a condition requiring careful medical management to prevent future thrombotic events.