Proteins in the blood of some people with autoimmune conditions such as systemic lupus erythematosus (SLE or lupus). Testing the blood for antinuclear antibodies (ANAs) can help to diagnose these conditions.
Antibodies are normal immune-system cells that recognize and attack foreign substances in the body. However, in people with autoimmune conditions, antibodies can turn against the body and mistakenly attack the body’s own tissues. ANAs target normal proteins in the nucleus of a cell. In the case of lupus, the ANAs can affect cells in virtually any part of the body, including skin, joints, kidneys, and blood, helping to bring about the classic symptoms of lupus — skin rashes and sores, sensitivity to the sun, achy or swollen joints, kidney problems, blood disorders, and fatigue.
The ANA test is used to clarify a diagnosis in people who show several symptoms of lupus or another autoimmune disorder. About 95% of people with lupus test positive for ANA. However, only about 11% to 13% of people with positive tests for ANA have lupus, and people with a number of other conditions — among them Sjögren syndrome (a condition that causes dry mouth and eyes), scleroderma (an autoimmune condition that can affect the skin, joints, blood vessels, and internal organs), and rheumatoid arthritis — frequently test positive for ANA. Healthy people may test positive for ANA as well. A positive ANA test therefore does not necessarily mean that someone has lupus. (However, a negative test strongly suggests that a person does not have lupus.) Doctors must rely on an individual’s description of symptoms and a careful examination in addition to blood tests to make an accurate diagnosis.