Autoimmune and ANA Testing: What Antinuclear Antibody Blood Tests Can Tell You

Key takeaways

• ANA testing detects autoantibodies directed against components of the cell nucleus.
• A positive ANA result is not by itself a diagnosis of an autoimmune disease.
• ANA tests are usually ordered alongside a person's symptoms, physical exam, and other laboratory tests.
• A negative ANA does not completely rule out every autoimmune condition, and a positive ANA does not confirm one.

What Is an ANA Test?

An antinuclear antibody (ANA) test is a blood test that looks for antibodies that target the body's own cell nuclei. Antibodies are proteins the immune system normally makes to recognize foreign invaders such as bacteria and viruses. In some people, the immune system produces antibodies that recognize normal cellular components instead, and these are called autoantibodies. The ANA test is a screening tool that can detect many of these nuclear-targeting autoantibodies at once.

The test is most often used when a healthcare provider suspects an autoimmune disease, particularly systemic lupus erythematosus (SLE). ANA testing may also be considered in the evaluation of conditions such as Sjögren's syndrome, systemic sclerosis, and mixed connective tissue disease. Because many different autoantibodies can produce a positive ANA, the result is interpreted together with symptoms and additional, more specific tests.

How ANA Testing Is Performed and Reported

ANA testing is performed on a blood sample, usually drawn from a vein in the arm. In many laboratories, the sample is analyzed using an indirect immunofluorescence assay, in which the person's antibodies are applied to cells and any binding is detected with a fluorescent marker. Some laboratories use other methods, such as enzyme-linked immunosorbent assay (ELISA) or multiplex immunoassays. Each method has its own performance characteristics, which is one reason results should be interpreted by a clinician familiar with the testing method used.

Results are often reported as a titer, such as 1:40, 1:80, 1:160, or 1:320. A higher titer means the sample had to be diluted more times before antibodies were no longer detectable. Some reports also describe a staining pattern, such as homogeneous, speckled, or nucleolar, which can offer clues about which autoantibodies may be present. Titers and patterns are not diagnoses on their own; they are pieces of information that a provider weighs along with clinical findings.

What a Positive or Negative ANA Result Means

A positive ANA result means that autoantibodies against nuclear components were detected in the blood. This finding is relatively common and can occur in people who do not have an autoimmune disease, especially at low titers. Some healthy individuals, particularly older adults, may have a low-positive ANA. Certain medications, infections, and other medical conditions can also be associated with a positive ANA. Because of this, a positive result must be considered in the context of the person's symptoms and other test results.

A negative ANA result means that no antinuclear antibodies were detected at the laboratory's reporting threshold. For conditions such as systemic lupus erythematosus, a negative ANA makes the diagnosis less likely, and ANA testing is often used as part of the initial workup. However, a negative result does not exclude every autoimmune disease, because some conditions are associated with antibodies that are not detected by the standard ANA test or may be negative in a subset of patients.

How ANA Testing Fits Into an Autoimmune Evaluation

ANA testing is rarely ordered in isolation. A healthcare provider typically considers a person's symptoms, medical history, family history, physical examination, and other laboratory findings. If the ANA is positive and the clinical picture suggests an autoimmune condition, more specific antibody tests may be ordered. Examples include anti-double-stranded DNA and anti-Smith antibodies for lupus, anti-SSA and anti-SSB antibodies for Sjögren's syndrome, and anti-centromere or anti-topoisomerase I antibodies for systemic sclerosis.

Follow-up testing helps clarify what a positive ANA might mean, because different autoantibodies are associated with different conditions. In some cases, a provider may repeat ANA testing over time or monitor symptoms rather than relying on a single result. The goal is to combine the ANA result with other information to reach an accurate diagnosis and appropriate management plan, rather than treating a laboratory value alone.

Frequently Asked Questions

Sources

• MedlinePlus: Antinuclear Antibody (ANA) Test
• National Institute of Arthritis and Musculoskeletal and Skin Diseases: Lupus Diagnosis
• Centers for Disease Control and Prevention: Lupus
• Mayo Clinic: Antinuclear Antibody Test
• National Library of Medicine: Autoimmune Diseases