From the Guidelines
The ANA lab test is considered positive when it detects autoantibodies at a titer ≥1:80 by the indirect immunofluorescence test on HEp-2 cells, as per the EULAR/ACR 2019 classification criteria 1.
Interpretation of Results
The results of the ANA lab test are typically reported as a titer (level of antibody concentration) and a pattern (how antibodies appear under microscope).
- A positive result suggests the immune system may be attacking the body's own tissues, but it doesn't automatically confirm disease.
- Up to 15% of healthy individuals may have positive ANA tests at low titers.
- If ANA is positive, additional specific antibody tests are usually ordered to narrow down the diagnosis.
Clinical Utility
The ANA test is particularly useful for diagnosing systemic lupus erythematosus (SLE), but is also associated with other autoimmune conditions like Sjögren's syndrome, scleroderma, rheumatoid arthritis, and mixed connective tissue disease.
- The test requires a simple blood draw and doesn't need special preparation.
- It's essential to understand that ANA testing is most valuable when interpreted alongside clinical symptoms and other laboratory findings, not as a standalone diagnostic tool 1.
Limitations and Considerations
The specificity of ANA detection for SLE is 74.7% (IC 95%: 66.7% - 81.3%) when using a cut-off point of 1:80, which is lower than the specificity observed when using the EULAR/ACR 2019 criteria as a whole 1.
- ANA tests are requested in various scenarios, including diagnosis, clinical algorithms to rule out autoimmune disorders, and treatment evaluation unrelated to SLE.
- The high sensitivity and relatively low specificity of ANA tests make them an appropriate entry criterion for the EULAR/ACR 2019 classification, but caution is necessary when using them for diagnosis due to their limited specificity 1.
From the Research
Results of the Antinuclear Antibody (ANA) Lab Test
The results of the ANA lab test can indicate the presence of antinuclear antibodies in a patient's blood, which can be associated with various conditions, including:
- Autoimmune diseases, such as systemic lupus erythematosus (SLE) 2, 3, 4
- Non-autoimmune inflammatory diseases, including acute and chronic infections 2, 5
- Non-rheumatic diseases, such as atopic dermatitis and immune disorders 6
- Chronic bacterial or viral infections 5, 6
- Hematological malignancies 6
Interpretation of ANA Test Results
The interpretation of ANA test results requires careful consideration of the patient's clinical symptoms and medical history, as a positive result can have various implications, including:
- Increased risk of autoimmune diseases, such as lupus and Raynaud's syndrome 3
- Decreased risk of certain non-autoimmune diseases, such as hepatitis C and tobacco use disorders 3
- Association with certain infectious diseases, such as Mycobacterium tuberculosis and Treponema pallidum 5
ANA Subtypes and Staining Patterns
The identification of ANA subtypes and staining patterns can provide valuable information for diagnosing specific autoimmune diseases, including: