Antinuclear antibodies (ANA) are a group of autoantibodies produced by a person’s immune system when it fails to adequately distinguish between “self” and “nonself.” The ANA test detects these autoantibodies in the blood.
ANA react with components of the body’s own healthy cells and cause signs and symptoms such as tissue and organ inflammation, joint and muscle pain, and fatigue. ANA specifically target substances found in the nucleus of a cell, hence the name “antinuclear.” They probably do not damage living cells because they cannot access their nuclei. However, ANA can cause damage to tissue by reacting with nuclear substances when they are released from injured or dying cells.
The ANA test is one of the primary tests for helping to diagnose a suspected autoimmune disorder or rule out other conditions with similar signs and symptoms. The ANA test may be positive with several autoimmune disorders. Patients with the autoimmune disorder systemic lupus erythematosus (SLE) are almost always positive for ANA, but the percentage of patients with other autoimmune disorders who have positive ANA results varies. Also, a significant number of patients with a variety of other types of disorders (and even some heathy people) may be positive for ANA, especially at low levels.