Possible causes of a positive antinuclear antibody, or ANA, test include the presence of an autoimmune disease in the connective tissue or other organs, reports WebMD. Other diseases, infections and prescription drugs can give positive results, adds About.com. A small percentage of healthy people also test positive in ANA tests.
An ANA test looks for antibodies in the immune system that attack and damage the body's own tissues, explains WebMD. Doctors use the test along with a physical examination and analysis of other symptoms to detect autoimmune diseases in connective tissue, such as rheumatoid arthritis, lupus and scleroderma. The test may also indicate diseases in the liver, thyroid and heart. Because viral infections and prescription drugs that patients take for heart disease, high blood pressure, tuberculosis and other ailments also yield positive test results, doctors must combine ANA tests with other diagnostic tests.
Almost all patients who have lupus or scleroderma have positive results in ANA tests, but the results are less definitive for other autoimmune diseases, according to About.com. Other non-autoimmune diseases that may give positive ANA results include hormonal diseases, gastrointestinal diseases, lung diseases and cancer. Elderly people and those with rheumatic disease in their family histories tend to have a higher percentage of positive ANA results. About 5 percent of the healthy population tests positive for antinuclear antibodies as of 2015.