ANA is the abbreviation for
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
Antibody Antibodies are seen as blobs of green fluorescence
- see picturesbelow.
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
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
important thing you need to know about
a positive ANA is:
it doesn't mean you have lupus.
because there are many other causes of a positive ANA. However a
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
likely as you age and if you are female.
Causes of a Positive ANA
Normal finding (aging and being female)
Polymyositis / Dermatomyositis
Chronic liver disease
Chronic lung disease
Some drugs (e.g. minocycline)
Some infections(e.g. mononucleosis)
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.