From the Guidelines
Testing for autoimmune conditions should always begin with a thorough clinical evaluation, followed by the antinuclear antibody (ANA) test as the initial screening tool, and then more specific antibody tests based on symptoms, as recommended by the most recent evidence 1. When evaluating patients for autoimmune diseases, it is essential to consider the clinical context and use a combination of blood tests to look for specific antibodies and inflammatory markers.
- The ANA test is the most common initial test, serving as a screening tool for several autoimmune diseases like lupus, rheumatoid arthritis, and Sjögren's syndrome.
- If the ANA is positive, more specific antibody tests are usually ordered based on symptoms, such as anti-dsDNA for lupus, rheumatoid factor and anti-CCP for rheumatoid arthritis, or anti-SSA/SSB for Sjögren's syndrome.
- Other useful tests include complete blood count, erythrocyte sedimentation rate (ESR), and C-reactive protein (CRP) to assess inflammation levels.
- Complement levels (C3, C4) may also be checked as they are often low in active autoimmune disease.
- For organ-specific autoimmune conditions, targeted tests are available, such as thyroid antibodies for autoimmune thyroid disease or tissue transglutaminase antibodies for celiac disease. It's crucial to interpret these tests alongside clinical symptoms, as some people may have positive antibody tests without having an autoimmune disease, while others with autoimmune conditions might initially test negative, as noted in studies 1. The most recent evidence suggests that the use of a 1:160 dilution as the cut-off point for ANA positivity can increase the positive likelihood ratio and diagnostic performance, especially in selected populations 1. In addition, the EULAR/ACR 2019 classification recommends ANA detection using the IFI or a solid-phase ANA screening immunoassay (SPA) with at least equivalent performance, highlighting the importance of standardization and interpretation of results in the context of clinical symptoms 1.
From the Research
Testing for Autoimmune Diseases
- Autoantibodies can help clinicians detect autoimmune diseases early and monitor treatment response 2
- Laboratory testing, including complete blood count, comprehensive metabolic panel, and autoantibody measurement, is valuable in evaluating suspected autoimmune diseases 3
- Autoantibody positivity alone does not confirm a diagnosis, and absence of autoantibodies does not exclude diagnosis 2
Components of Laboratory Examination
- Complete blood count with differential 3
- Comprehensive metabolic panel 3
- Measurement of inflammatory markers and autoantibodies 3
- Flow cytometry 3
- Neutrophil-to-Lymphocyte Ratio (NLR) can assess disease activity and response to treatment in Rheumatoid Arthritis (RA) 4
- Mean Platelet Volume (MPV) and NLR can determine the prognosis of renal involvement in Systemic lupus erythematosus (SLE) 4
Interpretation of Test Results
- Interpretation of sensitivity, specificity, and likelihood ratios is crucial for proper laboratory evaluation 2
- A thorough history and physical examination, as well as laboratory evaluation, are recommended to elucidate the cause of a positive test result 5
- Knowledge of the mean titer and presence or absence of specific autoantibodies can help predict the nature of the disease and response to therapy 6