From the Guidelines
When ordering an ANA test, it is recommended to couple it with an anti-extractable nuclear antigen (anti-ENA) panel to determine autoimmune involvement in a patient. This approach is supported by a recent expert panel proposal published in Autoimmunity Reviews in 2023 1. The anti-ENA panel typically includes tests for autoantibodies against specific targets such as chromatin, ribosomal P protein, spliceosome small nuclear ribonucleoproteins (Smith), Sjögren syndrome type A antigen (Ro), Sjögren syndrome type B antigen (La), and U1-ribonucleoprotein.
Key points to consider when ordering these tests include:
- The anti-ENA panel helps to confirm the diagnosis and provides more specific information about the autoimmune disease present
- A positive ANA result alone has limited specificity, and additional testing is necessary to determine the underlying condition
- The anti-ENA panel can help to identify specific autoimmune diseases such as systemic lupus erythematosus, Sjögren's syndrome, and mixed connective tissue disease
The recommendation to couple ANA with anti-ENA testing is based on the latest evidence from an expert panel in the field of autoimmunity 1. This approach allows for a more precise diagnosis and targeted treatment of autoimmune conditions, ultimately improving patient outcomes in terms of morbidity, mortality, and quality of life.
From the Research
Laboratory Tests for Autoimmune Involvement
To determine autoimmune involvement in a patient, the Antinuclear Antibody (ANA) lab order can be coupled with other laboratory tests. The following tests are relevant:
- Extractable nuclear antigens (ENAs) panel, which includes anti-Ro/SSA, anti-La/SSB, anti-U1-RNP, anti-Jo-1, and anti-Sm antibodies 2
- Anti-Ro/SSA and anti-La/SSB antibodies, which are commonly found in patients with systemic lupus erythematosus (SLE), Sjögren's syndrome (SS), and other autoimmune diseases 3, 4, 5
- Rheumatoid factor (RF) and anti-citrullinated protein antibody (ACPA) tests, which are relevant in rheumatoid arthritis (RA) patients 2
Rationale for Test Selection
The selection of laboratory tests to couple with ANA depends on the clinical presentation and suspected autoimmune disease. For example:
- In patients with suspected SLE or SS, anti-Ro/SSA and anti-La/SSB antibodies should be tested 3, 4
- In patients with suspected RA, RF, ACPA, and anti-ENAs (including anti-Ro/SSA, anti-La/SSB, and anti-Jo-1) should be tested 2
- In patients with suspected autoimmune disease, a comprehensive laboratory evaluation, including a complete blood count, comprehensive metabolic panel, measurement of inflammatory markers, and autoantibody tests, should be performed 6
Test Interpretation
The interpretation of laboratory test results should be done in conjunction with clinical evaluation and other diagnostic criteria. For example: