Lab Test: Antinuclear Antibody, ANA Level (Blood)
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- Measurement of antinuclear antibodies (ANA) in serum for evaluation of autoimmune and connective tissue diseases.
- Monitoring disease activity in multiple sclerosis - ANA are detected in 10% to 80% of MS patients. MS patients with elevated anticardiolipin antibodies display atypical features and slower disease progression. These patients may be more prone to thrombotic events.
- Suspected and known rheumatoid arthritis - ANA assays are positive in up to 30% of RA patients with a positive rheumatoid factor test. However, these ANAs are not directed against specific nuclear antigens that are usually tested in the ANA profile.
- Suspected autoimmune thyroid disease - presence of ANAs nay indicate this disease.
- Suspected scleroderma (systemic sclerosis) - about 40% of patients with scleroderma and associated conditions will test positive for ANA. In patients with progressive systemic sclerosis, approximately 96% have ANA when the Hep-2 substrate is used, and the ANA serotype variant SCL-70 has been found in 20% of these patients.
- Suspected Sj1/2f-gren's syndrome - positive test is a dilution greater than or equal to 1 in 40.
- Suspected systemic lupus erythematosus - an abnormal titer of ANA by immunofluorescence or an equivalent assay is 1 of 11 ACR criteria for the diagnosis of SLE. P patient with 4 of the 11 criteria can be diagnosed with SLE with a specificity of approximately 95% and a sensitivity of 85%. ANA is the best single test for ruling out the diagnosis of SLE. An abnormal ANA titer is present in 76% of patients at SLE onset and in 94% of patients at any time after SLE onset.
- Anticentronere antibody - used to diagnose CREST syndrome
- Anti-DNA antibody - used to diagnose SLE
- Antiextractable nuclear antigen (ENA) - used to diagnose SLE and mixed connective tissue disease
- Antiscleroderma antibody - used to diagnose scleroderma
- Drugs that may cause a false-positive ANA test include: acetazolamide, aminosalicylic acid, chlorothiazides, chlorprothixene, griseofulvin, hydralazine, penicillin, phenylbutazone, phenytoin, procainamide, streptomycin, sulfonamides, and tetracyclines.
- Drugs that may cause a false-negative test include steroids.
- Collect a venous blood sample. Apply pressure or a pressure dressing to the venipuncture site and assess site for bleeding.
- Explain the procedure to the patient and tell them that no fasting or preparation is required.
- Because they are usually immunocompromised, patients with an autoimmune disease should be instructed to check for signs of infection at the venipuncture site. These patients often take steroids that further compromise their immune system.
Autoantibodies are directed to nuclear material (ANAs) or to cytoplasmic material (anticytoplasmic antibodies). ANA is a group of protein antibodies that react against cellular nuclear material and are quite sensitive for detecting SLE. Positive results occur in approximately 95% of patients with this disease; however, many other rheumatic diseases are also associated with ANA. Therefore, it is not a specific test for SLE. It can be tested as a specific antibody or as a group with nonspecific antigens.
ANA tests are performed using different assays (indirect immunofluorescence microscopy or by enzyme-linked immunosorbent assay [ELISA]) and results are reported as a titer with a particular type of immunofluorescence pattern (when positive).
In general, the higher the titer of a certain ANA antibody known to be associated with a certain autoimmune disease, the more likely that disease exists and the more active the disease is.
Accuracy of the ANA test depends on each laboratory using a cutoff based on their conditions of assay. Substantial variability exists between laboratories due to immunologic reagents and laboratory conditions.
The ANA test is frequently over-ordered. The test has excellent sensitivity and acceptable specificity, but its positive predictive value is often low because of overuse in low-risk populations, with a false-positive of 20% or more.
Several patterns of fluorescence in the ANA can be seen microscopically; however, these patterns are not diagnostic of different related diseases.
MESH Terms & Keywords
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