Antinuclear Antibody
A positive ANA does not diagnose an autoimmune disease nor does a negative result exclude it; however, the ANA is positive in 99% of patients with Systemic Lupus Erythematosus, which means a negative result strongly argues against such a diagnosis.
ANA can be positive by definition in 5% of the healthy population, typically in titers less than 1:320. Up to 20% of healthy relatives of patients with rheumatic disease and up to 75% of healthy individuals older than 70 will have a positive ANA (typically less than 1:80 with a speckled or homogenous pattern).
Other conditions associated include:
- thyroid disease
- chronic infections including TB/viral hepatitis
- subacute bacterial endocarditis
- malignancies
- any of the auto-immune disease
- multiple sclerosis
- silicone breast implants.
In the absence of physical or biochemical evidence of pathology, a positive ANA is not clinically useful, i.e you do not treat the lab result, only symptoms or a disease.
Since there are no labs tests that prove you do or do not have a diagnosis of Lupus or other rheumatological diseases, a frequent reason for referral to a rheumatologist is to determine the cause of a positive ANA.