It is a test that is performed by applying the patient's serum to a slide which has been layered with tissue culture cells- usually a cell line called Hep2 (originally derived from a patient with an epithelial cell tumor). If the serum has antibodies that react with cell nuclei they will "stick" to the cells and can be detected with a second antibody - labeled with a fluorescent marker.  When viewed under a microscope, illuminated with an ultra-violet light, the

Antinuclear Antibody Antibodies are seen as blobs of green fluorescence - see picture below.

This is what is meant by a positive ANA.  Each laboratory has to determine how much the patient's serum must be diluted before it is reacted with the cells - as "neat" serum often gives a positive ANA test. Thus a positive test is defined as the lowest dilution that would be expected to produce green fluorescence in a patient with disease. This is usually referred to as a titer. For instance, a titer greater than a dilution of 1 in 40 might be the dilution separating a normal serum from a diseased serum. This is usually seen on the lab report as Positive > 1:40. The higher the titer, the more likely the patient has an immune disease such as lupus (SLE).

Causes of a Positive ANA

Lupus (SLE)

Scleroderma

Polymyositis / Dermatomyositis

Rheumatoid arthritis

Sjogren's syndrome

Normal finding (with aging and being female)

Some drugs (procainamide, hydrallazine, isoniazid, antibiotics)

Infectious mononucleosis (mono) and other infections

Chronic liver disease    

Do you have lupus?

The most important thing you need to know about a positive ANA is: it doesn't mean you have lupus.

This is because there are many other causes of a positive ANA.  However a negative ANA
virtually rules out the possibility of having lupus.  The possible causes of a positive ANA are given in the table to the right. Importantly some normal individuals have a positive ANA - this is more likelyas you age and if you are female.

The diagnosis of lupus is based on the finding of 4 or more findings out of 11 features. A positive ANA is just one of these findings. Unfortunately some fibromyalgia patients are incorrectly diagnosed as having SLE.