What Is An ANA (antinuclear antibody) Test?

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What Is An ANA (antinuclear antibody) Test?

http://arthritis.about.com/od/diagnostic/a/ana.htm

About.com Health's Disease and Condition content is reviewed by Kate

Grossman, MD

ANA test helps diagnose autoimmune disease.

In order to understand the ANA (antinuclear antibody) test, it is first

important to understand different types of antibodies.

Antibodies are proteins, produced by white blood cells, which normally

circulate in the blood to defend against foreign invaders such as bacteria,

viruses, and toxins.

Autoantibodies, instead of acting against foreign invaders as normal

antibodies do, attack the body's own cells.

Antinuclear antibodies are a unique group of autoantibodies that have the

ability to attack structures in the nucleus of cells. The nucleus of a cell

contains genetic material referred to as DNA (deoxyribonucleic acid).

There is an ANA (antinuclear antibody) test which can be performed on a

patient's blood sample as part of the diagnostic process to detect certain

autoimmune diseases.

ANA (Antinuclear Antibody) Test

To perform the ANA (antinuclear antibody) test, sometimes called FANA

(fluorescent antinuclear antibody test), a blood sample is drawn from the

patient and sent to the lab for testing.

Serum from the patient's blood specimen is added to microscope slides which

have commerically prepared cells on the slide surface.

If the patient's serum contains antinuclear antibodies (ANA), they bind to

the cells (specifically the nuclei of the cells) on the slide.

A second antibody, commercially tagged with a fluorescent dye, is added to

the mix of patient's serum and commercially prepared cells on the slide. The

second (fluorescent) antibody attaches to the serum antibodies and cells

which have bound together. When viewed under an ultraviolet microscope,

antinuclear antibodies appear as fluorescent cells.

If fluorescent cells are observed, the ANA (antinuclear antibody) test is

considered positive.

If fluorescent cells are not observed, the ANA (antinuclear antibody) test

is considered negative.

How is the ANA titer determined?

A titer is determined by repeating the positive test with serial dilutions

until the test yields a negative result. The last dilution which yields a

positive result (flourescence) is the titer which gets reported. For

example, if a titer performed for a positive ANA test is:

1:10 positive

1:20 positive

1:40 positive

1:80 positive

1:160 positive

1:320 negative

The reported titer in our example is 1:160.

Three parts of an ANA report

An ANA report has three parts:

positive or negative

if positive, a titer is determined and reported

the pattern of flourescence is reported

What is the significance of the ANA pattern?

ANA titers and patterns can vary between laboratory testing sites, perhaps

because of variation in methodology used. These are the commonly recognized

patterns:

Homogeneous - total nuclear fluorescence due to antibody directed against

nucleoprotein. Common in SLE (lupus).

Peripheral - fluorescence occurs at edges of nucleus in a shaggy appearance.

Anti-DNA antibodies cause this pattern. Also common in SLE (lupus).

Speckled - results from antibody directed against different nuclear

antigens.

Nucleolar - results from antibody directed against a specific RNA

configuration of the nucleolus or antibody specific for proteins necessary

for maturation of nucleolar RNA. Seen in patients with systemic sclerosis.

What does a positive ANA result mean?

ANAs are found in patients who have various autoimmune diseases, but not

only autoimmune diseases. ANAs can be found also in patients with

infections, cancer, lung diseases, gastrointestinal diseases, hormonal

diseases, blood diseases, skin diseases, and in elderly people or people

with a family history of rheumatic disease. ANAs are actually found in about

5% of the normal population.

The ANA results are just one factor in diagnosing, and must be considered

together with the patient's clinical symptoms and other diagnostic tests.

Medical history also plays a role because some prescription drugs can cause

" drug-induced ANAs " .

What is the incidence of ANA in various diseases or conditions?

Statistically speaking the incidence of positive ANA (in percent) per

conditon is:

Systemic lupus erythematosus (lupus or SLE) - over 95%

Progressive systemic sclerosis (scleroderma) - 60-90%

Rheumatoid Arthritis - 25-30%

Sjogren's syndrome - 40-70%

Felty's syndrome - 100%

Juvenile arthritis - 15-30%

Subsets of the ANA (antinuclear antibody) test are sometimes used to

determine the specific autoimmune disease. For this purpose, a doctor may

order anti-dsDNA, anti-Sm, Sjogren's sydrome antigens(SSA, SSB), Scl-70

antibodies, anti-centromere, anti-histone, and anti-RN.

The ANA (antinuclear anibody) test is complex, but the results (positive or

negative, titer, pattern) and possible subset test results can give

physicians valuable diagnostic information.