Understanding the ANA Blood Test (Antinuclear Antibody Test)

An ANA blood test (antinuclear antibody test) is usually performed on a blood sample as part of the diagnostic process for certain autoimmune diseases. It is usually ordered along with other blood tests, such as CBC and ESR—and all of the results are considered together.

The ANA blood test measures a certain type of antibodies.

• Antibodies are proteins produced by white blood cells, which normally circulate in the blood to defend against harmful materials, such as bacteria, viruses, and toxins.
• Autoantibodies attack the body's own cells, instead of acting against harmful substances. This is abnormal and causes health problems.
• 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, known as DNA (deoxyribonucleic acid).

How the Test Is Performed

If you are having an ANA blood test, sometimes called FANA (fluorescent antinuclear antibody test), your blood sample is drawn and sent to the lab for testing.

Serum from the blood specimen is added to microscope slides which have commercially prepared cells on the slide surface. If your serum contains antinuclear antibodies, they would 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 serum and commercially prepared cells on the slide. The second (fluorescent) antibody attaches to the serum antibodies and cells which have bound together. When the slide is viewed under an ultraviolet microscope, antinuclear antibodies appear as fluorescent cells.

• If fluorescent cells are observed, the ANA blood test result is positive.
• If fluorescent cells are not observed, the ANA blood test result is negative.

ANA Blood Test Report

An ANA blood test report has three parts:

• Positive or negative for ANA
• If positive, a titer that reflects the amount or concentration is determined and reported
• The pattern of fluorescence is reported

ANA Titer

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 (i.e., fluorescence observed under the microscope) is the titer that is reported.

Here is an example:

Serial Dilutions:
1:10 positive
1:20 positive
1:40 positive
1:80 positive
1:160 positive (titer reported as 1:160)
1:320 negative

The Significance of ANA Pattern

ANA titers and patterns can vary between laboratory testing sites due to variations in the methodology used.

The commonly recognized patterns include:

• Homogeneous: Total nuclear fluorescence due to an antibody directed against DNA or histone proteins. Common in systemic lupus erythematosus.
• Peripheral: Fluorescence occurs at the edges of the nucleus in a shaggy appearance. Anti-DNA and anti-nuclear envelope antibodies cause this pattern. Seen in systemic lupus erythematosus.
• Speckled: Speckled fluorescence due to an antibody directed against different nuclear antigens. This pattern is common in lupus and other connective tissue diseases, such as Sjogren's syndrome.
• Nucleolar: Formed from antibodies directed against specific proteins involved in the maturation of RNA. Seen in people with scleroderma (systemic sclerosis).

What Does a Positive ANA Blood Test Result Mean?

Antinuclear antibodies are found in people with various autoimmune diseases, but they can also be high in people who have other conditions.

Antinuclear antibodies can also be found in people with:

• Infections
• Cancer
• Lung diseases
• Gastrointestinal diseases
• Hormonal diseases
• Blood diseases
• Skin diseases
• Advanced age
• A family history of rheumatic disease

Some prescription drugs can cause drug-induced antinuclear antibodies.

The prevalence of antinuclear antibodies in healthy people is estimated to be 3-15%, but is strongly age-dependent, and increases to 10-37% in healthy people over age 65.

Incidence of ANA in Various Diseases

Statistically-speaking, the incidence of positive ANA test results (in percent per condition) is:

• Systemic lupus erythematosus (lupus or SLE): Over 95 percent
• Progressive systemic sclerosis (scleroderma): 60 to 90 percent
• Rheumatoid arthritis: 25 to 30 percent
• Sjogren's syndrome: Up to 80 percent
• Felty's syndrome: Over 75 percent
• Juvenile arthritis: 15 to 30 percent

Subsets of the ANA blood tests are sometimes used to determine the specific autoimmune disease. For this purpose, a doctor may order anti-dsDNA, anti-Sm, Sjogren's syndrome antigens (SSA, SSB), Scl-70 antibodies, anti-centromere, anti-histone, and anti-RNP.

A Word From Verywell

The ANA blood test can seem complicated. The results—positive or negative, titer, pattern, and subset test results—can provide healthcare providers with valuable clues to help diagnose many medical conditions. The results are considered along with your health history and results of other tests. Rest assured that even if the road to getting a diagnosis takes longer than you would like—there are treatments to help control your symptoms and your underlying condition.