It is important to understand that positive ANA results may be found in healthy people without autoimmune disease, particularly the elderly and pregnant people. Therefore positive ANA results in elderly and pregnant patients must be interpreted cautiously making use of all of the clinical information about the patient. Positive ANA results can also be seen in some viral infections or inflammatory conditions that are not autoimmune diseases, so it is important that test results are interpreted with caution. However, more specific tests can be done to help interpret the positive ANA results (see below).
A positive test result together with relevant clinical symptoms suggests the presence of an autoimmune disease and the doctor will then carry out further more specific tests (e.g ENA and dsDNA antibody tests) and consider the clinical history of the patient to assist in making a final diagnosis. Positive ANA results may appear months or years before signs of disease appear, which is a further reason for careful interpretation of all positive ANA results.
About 95% of patients with SLE have a positive ANA test result. If a patient has symptoms of SLE, such as arthritis, a rash, and autoimmune thrombocytopenia (a low number of specialised blood cells called platelets), then they may have SLE. In such cases, a positive ANA result can be useful to support SLE diagnosis. If needed, additional highly specific tests, anti-dsDNA antibodies, and anti-SM antibodies, can help to show with more confidence that the condition is SLE.
A positive ANA test can also mean that the patient has drug-induced SLE-like syndrome. This condition is associated with the development of antibodies to parts of your DNA called histones. An anti-histone antibody test can be used to support the diagnosis of drug induced SLE-like syndrome.
Other conditions in which a positive ANA test result may be seen include:
- Sjögren’s syndrome: Between 50-75% of patients with this condition have a positive ANA test result. Your doctor may want to do two more specific tests, called anti- SSA and anti-SSB antibodies, to help confirm the diagnosis of Sjögren's
- Scleroderma: Around 90% of patients with scleroderma have a positive ANA test. Two forms of this condition exist called ‘limited’ and ‘diffuse’. The diffuse form is more severe. Patients with limited scleroderma may have anti-centromere antibodies, which give a distinctive pattern in the ANA test and are confirmed with a specific anti-centromere antibody test. Patients with diffuse scleroderma may have anti-Scl-70 antibodies.
- A positive result on the ANA test may also show up in patients with Raynaud’s disease, polymyositis, juvenile chronic arthritis, or antiphospholipid antibody syndrome, but a doctor needs to rely on clinical symptoms and history for diagnosis.
A negative ANA result makes SLE an unlikely diagnosis. However, because autoimmune diseases change over time, it may be worthwhile repeating the ANA test in the future. Apart from rare cases, further antibody (subset) testing is not necessary if a patient has a negative ANA result.
