What is an ANA (antinuclear antibody) test?

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What is an ANA (antinuclear antibody) test?

ANA test helps diagnose autoimmune disease.

Types of Antibodies

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.