The Antinuclear Antibody Test: What It Means
Diagnosing lupus is a complex process. It's not as simple as diagnosing a broken bone, strep throat, or pregnancy. In these conditions there are simple tests which, if positive, point to a single diagnosis. There is no single diagnostic test for lupus. There is a screening test called the ANA (anti-nuclear antibody) test which is often checked when a doctor suspects lupus.
If the ANA test comes back negative it is considered a normal result, and it is very good evidence against lupus as an explanation for the symptoms. If the ANA test result comes back above the normal range the test is said to be positive. A positive ANA test by itself is not proof of lupus.
Understanding the positive ANA test
What does a positive ANA mean? Unlike a pregnancy test, which if positive generally means only one thing, a positive ANA can mean many things. There are many illnesses and conditions associated with a positive ANA, including rheumatoid arthritis, Sjogren's syndrome, scleroderma, and lupus, as well as infectious diseases such as mononucleosis, subacute bacterial endocarditis, and autoimmune thyroid and liver disease.
Certain medications can cause a positive ANA, and many healthy people with no associated illness or condition have a positive ANA. In fact, about 5% of the general population will have a positive ANA. However, at least 95% of the people who have a positive ANA do not have lupus! A positive ANA test can sometimes run in families, even if family members have no evidence of lupus.
The ANA is only a test and, like a high cholesterol value, a positive ANA doesn't necessarily equate having a disease. A positive ANA is only an indicator which points in several possible directions, and indicates that further investigation and analysis may be needed.