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What is an ANA ?

ANA is the abbreviation for "Antinuclear Antibody"

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 pictures 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).

 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 following table. Importantly some normal individuals have a positive ANA - this is more likely as you age and if you are female.

Causes of a Positive ANA

Normal (aging and being female)
Lupus (SLE)
Polymyositis / Dermatomyositis
Sjogren's syndrome
Mixed connective tissue disease

Rheumatoid arthritis
Chronic liver disease
Chronic lung disease
Inflammatory bowel disease
Some drugs (e.g. minocycline)
Some infections(e.g. mononucleosis)

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.


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