ANA (Antinuclear Antibody) Test is a blood test used to detect the presence of autoimmune antibodies in the body. It is performed by taking a small sample of blood from the patient and analyzing it in a laboratory. The test measures the levels of antibodies that target the nucleus of a cell, which can indicate the presence of an autoimmune disease. The results of the test can help diagnose conditions such as lupus or rheumatoid arthritis.