The anti-cardiolipin (IgG) antibody test in serum measures the levels of anticardiolipin antibodies in the blood. This analysis is used to diagnose antiphospholipid syndrome, a condition that increases the risk of blood clots. It may be elevated in conditions such as lupus or antiphospholipid syndrome. A blood sample is usually taken in the morning, and a doctor should be consulted to understand the results and receive appropriate guidance.