From the Guidelines
If an ANA test is positive, reflex labs that should be ordered include anti-dsDNA, anti-ENA antibodies, and other specific tests based on clinical suspicion and ANA pattern, as recommended by international guidelines 1. When an ANA test is positive, it is essential to further evaluate for specific autoimmune conditions. The initial step is to report the pattern and the highest dilution to demonstrate reactivity, as this information can guide which specific antibody tests are most appropriate 1.
Recommended Reflex Labs
- Anti-dsDNA antibodies: especially if there is clinical suspicion of SLE, with methods like the Farr assay and CLIFT offering high clinical specificity 1
- Anti-ENA antibodies: including tests for specific ENA like anti-RNP, anti-SSA/Ro, anti-SSB/La, based on clinical suspicion and ANA pattern 1
- Other specific tests: such as anti-Scl-70, anti-centromere, anti-Jo-1, and anti-histone antibodies, depending on the clinical context and ANA pattern
Additional Considerations
- Complement levels (C3, C4, CH50) and rheumatoid factor may also be useful in evaluating autoimmune diseases 1
- A comprehensive metabolic panel with liver and kidney function tests can provide additional information on disease activity and organ involvement
- Clinical correlation with symptoms and additional laboratory findings is crucial for diagnosis, as ANA positivity can occur in healthy individuals, especially at low titers 1
From the Research
Reflex Labs to Order if ANA Positive
If a patient tests positive for Antinuclear Antibodies (ANA), several reflex labs can be ordered to further diagnose and manage the condition. These include:
- Anti-dsDNA antibodies: These antibodies are specific to Systemic Lupus Erythematosus (SLE) and can be used to monitor disease activity 2, 3, 4
- Anti-Sm antibodies: These antibodies are highly specific to SLE and can be used to diagnose the condition 3, 5, 4
- Anti-RNP antibodies: These antibodies can be used to diagnose Mixed Connective Tissue Disease (MCTD) and can also be present in SLE patients 3, 5, 4
- Anti-Ro/SS-A and anti-La/SS-B antibodies: These antibodies can be used to diagnose SLE and Sjögren's syndrome 3, 4
- Complement levels (C3 and C4): These levels can be used to monitor disease activity in SLE patients 2, 4
- Anti-histone antibodies: These antibodies can be used to diagnose drug-induced lupus 2
- Anti-C1q antibodies: These antibodies can be used to diagnose and monitor lupus nephritis 2
Laboratory Tests
The following laboratory tests can be used to detect these antibodies:
- Indirect immunofluorescence
- Enzyme-linked immunosorbent assay (ELISA)
- Counterimmunoelectrophoresis (CIE)
- Immunoblot
Interpretation of Results
The interpretation of ANA test results requires consideration of the disease context, antibody level, and titre-specific information 6. A positive ANA result should be followed by further testing to determine the specific antibody present and to diagnose the underlying condition.