Type of test : Blood

Normal findings

 Negative at 1:40 dilution

 Test explanation and related physiology

 ANA is a group of antinuclear antibodies used to diagnose systemic lupus erythematosus (SLE) and other autoimmune (rheumatic) diseases (Box A1). Some of the antibodies in this group are specific for SLE, and others are specific for other auto immune diseases. ANA can be tested as a specific antibody or as a group with nonspecific antigens (Box A2). The former is more specific, but testing ANA with less specific antigens may be an excellent preliminary test for those suspected of having autoimmune diseases.

 Because almost all patients with SLE develop autoantibodies, a negative ANA test result excludes the diagnosis. Positive results occur in approximately 95% of patients with this disease; however, many other rheumatic diseases (see Box A1) are also associated with ANA.

ANA tests are performed using different assays (indirect immunofluorescence microscopy or ELISA), and results are reported as a titer with a particular type of immunofluorescence pattern (when positive). Whereas low-level titers are considered negative, increased titers are positive and indicate an elevated concentration of antinuclear antibodies.

ANA shows up on indirect immunofluorescence as fluorescent patterns in cells that are fixed to a slide and are evaluated under a UV microscope. Different patterns are associated with a variety of autoimmune disorders. When combined with a more specific subtype of ANA (see Box A2), the pattern can increase specificity of the ANA subtypes for the various autoimmune diseases (Figure A2). An example of a positive result might be: “Positive at 1:320 dilution with a homogeneous pattern.”

As the disease becomes less active because of therapy, the ANA titers can be expected to fall (Table A1). In this text, the more commonly used ANA subtypes are separately discussed.

FIG. A2 Patterns of immunofluorescent staining of antinuclear antibodies and the diseases with which they are associated. SLE, Systemic lupus erythematosus.

About 95% of SLE patients have a positive ANA test result. If a patient also has symptoms of SLE (e.g., arthritis, rash, autoimmune thrombocytopenia), then he or she probably has SLE.

Interfering factors

* Drugs that may cause a false-positive ANA test include acetazolamide, aminosalicylic acid, chlorprothixene, chlorothia zide, griseofulvin, hydralazine, penicillin, phenylbutazone, phenytoin sodium, procainamide, streptomycin, sulfonamides, and tetracyclines.

* Drugs that may cause a false-negative test include steroids.

Procedure and patient care

• See inside front cover for Routine Blood Testing.

 • Fasting: no

 • Blood tube commonly used: red

 Abnormal findings

 Increased levels

- Systemic lupus erythematosus

- Rheumatoid arthritis

- Chronic hepatitis

-Periarteritis (polyarteritis) nodosa

- Dermatomyositis

- Scleroderma

-Infectious mononucleosis

-Raynaud disease

- Sjögren syndrome

- Other immune diseases

- Leukemia

-Myasthenia gravis

- Cirrhosis