ANA tests are performed using different assays (indirect immunofluorescence microscopy or by enzyme-linked immunoabsorbant assay - ELISA) and results are reported as a with a particular type of immunofluoroscence pattern (when positive). Low-level titres are often considered negative, while increased titres, such as 1:320, 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 that is evaluated under a microscope. Different patterns are associated with a variety of autoimmune disorders. Some of the more common patterns include:
- Homogenous (diffuse) - associated with SLE and mixed connective tissue disease
- Speckled - associated with SLE, Sjogren’s syndrome, scleroderma, polymyositis, rheumatoid arthritis, and mixed connective tissue disease
- Nucleolar - no definite disease association. In scleroderma, this pattern is more likely to be present than others (~70% of systemic scleroderma patients have positive ANA’s)
- Outline pattern (peripheral) - associated with SLE
An example of a positive result might be: ‘Positive at 1:320 dilution with a homogenous pattern.’
A positive ANA test result may suggest an autoimmune disease but further specific testing is required to assist in making a final diagnosis. ANA test results can be positive in people without any known autoimmune disease. While this is not common, the frequency of a ANA result increases as people get older.
Also, ANA may become positive before signs and symptoms of an autoimmune disease develop, so it may take time to tell the meaning of a positive ANA in a person who does not have symptoms. Most positive ANA results don't have significance, so physicians should reassure their patients but should also still be vigilant for development of signs and symptoms that might suggest an autoimmune disease. Perhaps as few as one in 75 people with a positive ANA will have SLE.
100% of SLE patients have a positive ANA test result at diagnosis using modern screening tests. Over time the ANA will fluctuate and may become negative on treatment. If a patient also has symptoms of SLE, such as arthritis, a rash, and autoimmune , then he or she probably has SLE. In cases such as these, a positive ANA result can be useful to support SLE diagnosis. Two subset tests for specific types of autoantibodies, such as anti-dsDNA and anti-SM, may be ordered to help confirm that the condition is SLE.
A positive ANA can also mean that the patient has drug-induced lupus. This condition is associated with the development of autoantibodies to histones, which are water soluble rich in the lysine and arginine. An anti-histone test may be ordered to support the diagnosis of drug-induced lupus.
Other conditions in which a positive ANA test result may be seen include:
- Sjögren’s syndrome: Most patients with this condition have a positive ANA test result. While this finding supports the diagnosis, a negative result does not rule it out. The doctor may want to test for two subsets of ANA: Anti-SS-A (Ro) and Anti-SS-B (La). The frequency of autoantibodies to SSA in patients with Sjögren’s is 95% or greater.
- Scleroderma: About 60% to 90% of patients with scleroderma have a positive ANA finding. In patients who may have this condition, ANA subset tests can help distinguished two forms of the disease - limited versus diffuse. The diffuse form is more severe. Limited disease is most closely associated with a pattern of ANA immunofluorescent staining called the anticentromere pattern (and the anticentromere test), while the diffuse form is associated with autoantibodies to the anti–Scl-70 as well as other antibodies.
- A positive result on the ANA also may show up in patients with Raynaud’s disease, rheumatoid arthritis, dermatomyositis, mixed connective tissue disease and other autoimmune conditions.
A doctor must rely on test results, clinical symptoms and the patient’s history for diagnosis. Because symptoms may come and go, it may take months or years to show a pattern that might suggest SLE or any of the other autoimmune diseases.
A negative ANA result excludes SLE as a diagnosis. It usually is not necessary to immediately repeat a negative ANA test, however, due to the episodic nature of autoimmune diseases, it may be worthwhile to repeat the ANA test at a future date.
In patients with some autoimmune disorders such as myositis, a negative ANA does not exclude the presence of specific antibodies.
Some drugs and infections as well as other conditions mentioned above can give a result for the ANA test.
About 3% - 5% of Caucasians may be positive for ANA and it may reach as high as 15% in healthy individuals over the age of 65.
Some medications may bring on a condition that includes SLE symptoms, called drug-induced lupus. When the drugs are stopped, the symptoms usually go away. Although many medications have been reported to cause drug-induced lupus, those most closely associated with this syndrome include hydralazine, isoniazid, procainamide and several anticonvulsants.