This test is essential for investigating the autoimmune cause of recurrent blood clots or miscarriages. It detects the IgG "memory" antibodies that mistakenly attack cardiolipins (part of your cell membranes). The presence of these long-term antibodies is a key marker for diagnosing Antiphospholipid Syndrome (APS). This test is almost always ordered with the IgM test for a complete picture. This simple blood test provides the 'historical' evidence your doctor needs to understand the root cause of these serious events.