What is the next step in screening for a patient who is Antinuclear Antibody (ANA) positive?

Next Steps in Screening for ANA Positive Patients

For patients with a positive Antinuclear Antibody (ANA) test, the next step should be testing for specific extractable nuclear antigens (ENA) and anti-dsDNA antibodies, with the specific tests guided by the ANA pattern and clinical suspicion. 1, 2

Initial Assessment of ANA Results

• The ANA pattern and titer should be reported and considered when determining follow-up testing, as different patterns suggest different autoantibodies and associated conditions 1, 2
• A screening dilution of 1:160 on conventional HEp-2 substrates is generally suitable for detecting clinically significant ANA in adult populations 1, 3
• Higher titers (>1:160) have greater clinical specificity (86.2%) while maintaining appropriate sensitivity (95.8%) for systemic autoimmune rheumatic diseases 1, 3

Pattern-Specific Follow-up Testing

For Nuclear Speckled Pattern:

• Test for specific ENAs including anti-SSA/Ro, anti-SSB/La (for Sjögren's syndrome), anti-Sm and anti-RNP (for SLE and mixed connective tissue disease), anti-Topo-1 (for systemic sclerosis), and anti-Jo-1 (for inflammatory myopathies) 2, 4
• A fine speckled pattern is associated with antibodies to SSA/Ro, SSB/La, Topoisomerase-1, commonly seen in SLE, Sjögren's syndrome, and systemic sclerosis 2, 4
• A coarse speckled pattern is associated with antibodies to U1-SnRNP, Sm, frequently seen in mixed connective tissue disease and SLE 2

For All ANA Positive Patterns:

• If SLE is clinically suspected, anti-dsDNA antibody testing is recommended regardless of the pattern 1
• For anti-dsDNA detection, the Crithidia luciliae immunofluorescence test (CLIFT) offers high clinical specificity, while solid phase assays (SPA) like ELISA provide higher sensitivity 1
• Results of anti-dsDNA antibody detection should be reported quantitatively 1

Algorithm for Follow-up Testing

1. For all ANA positive results:

   • Document pattern and titer 1
   • Determine if clinical suspicion exists for a specific autoimmune disease 1

2. If SLE is clinically suspected:

   • Perform anti-dsDNA testing using both SPA and CLIFT methods 1
   • If both tests are positive: SLE is very likely 1
   • If SPA positive but CLIFT negative: Evaluate in clinical context 1
   • If both tests are negative: SLE diagnosis is less likely 1

3. Based on ANA pattern:

   • Test for specific ENAs indicated by the pattern 1, 2
   • Report all ENA results separately, including negative findings 1

4. For monitoring disease activity:

   • In SLE patients, use the same method consistently for quantitative determination of anti-dsDNA antibodies 1

Important Caveats

• In cases of high clinical suspicion, specific antibody testing should be performed regardless of ANA result, as some autoantibodies (like anti-Jo-1, anti-ribosomal P, or anti-SSA/Ro) may be present in ANA-negative patients 1, 5
• Different laboratories use different methods and cutoffs for ANA testing, affecting result interpretation 1, 6
• A positive ANA alone is not diagnostic of any specific autoimmune disease and requires clinical correlation 2, 7
• The method used for antibody detection should always be included in the test result 1