What antibodies should be tested for in Rheumatoid Arthritis (RA) and Sjögren's syndrome?

Antibodies to Test for in Rheumatoid Arthritis and Sjögren's Syndrome

For rheumatoid arthritis (RA), test for rheumatoid factor (RF) and anti-citrullinated protein antibodies (anti-CCP), while for Sjögren's syndrome, test for anti-nuclear antibodies (ANA) with specific focus on anti-SSA/Ro and anti-SSB/La antibodies. 1, 2

Rheumatoid Arthritis Antibody Testing

Primary Antibodies

• Rheumatoid Factor (RF)

  • Sensitivity: approximately 60%
  • Specificity: approximately 70%
  • Important component of the 2010 ACR/EULAR classification criteria 2

• Anti-Citrullinated Protein Antibodies (anti-CCP)

  • Higher specificity than RF (>95%)
  • Particularly important when RF is negative
  • Strong predictor of erosive disease 2

Supporting Tests

• Inflammatory Markers
  • C-reactive protein (CRP)
  • Erythrocyte sedimentation rate (ESR)
  • Used to assess disease activity rather than for diagnosis 2

Sjögren's Syndrome Antibody Testing

Primary Antibodies

• Anti-Nuclear Antibodies (ANA)

  • First-level screening test using indirect immunofluorescent assay (IIFA) on HEp-2 cells 1
  • Patterns should be reported according to standardized terminology
  • Typical pattern: fine speckled pattern 1

• Anti-SSA/Ro Antibodies

  • Present in 60-70% of primary Sjögren's syndrome patients 3
  • Associated with earlier disease onset and extraglandular manifestations
  • Should be tested even if ANA is negative 1

• Anti-SSB/La Antibodies

  • Often co-exists with anti-SSA/Ro
  • Less sensitive but more specific for Sjögren's syndrome 3

Additional Antibodies to Consider

• Anti-alpha-fodrin antibodies
  • Limited diagnostic value compared to anti-SSA/Ro and anti-SSB/La 4
  • Not routinely recommended for initial screening

Testing Algorithm

For Suspected Rheumatoid Arthritis:

1. Order RF and anti-CCP antibodies simultaneously
2. Include inflammatory markers (ESR, CRP)
3. Consider complete blood count, liver and kidney function tests

For Suspected Sjögren's Syndrome:

1. Begin with ANA by IIFA on HEp-2 cells
2. Regardless of ANA result, test for anti-SSA/Ro and anti-SSB/La antibodies
3. Report ANA pattern and titer if positive

Overlap Considerations

When both conditions are suspected:

• Test for the complete panel of antibodies (RF, anti-CCP, ANA, anti-SSA/Ro, anti-SSB/La)
• Positive anti-CCP in Sjögren's syndrome patients may predict progression to RA (odds ratio 2.5) 5
• Anti-SSA/Ro antibodies can be present in RA patients and may influence treatment response 6

Important Caveats

• ANA testing is primarily for diagnostic purposes, not for monitoring disease progression 1
• Normal inflammatory markers do not rule out RA if clinical suspicion is high (approximately 40% of RA patients may have normal levels) 2
• Approximately 30% of RA patients have negative RF or anti-CCP tests, emphasizing the importance of clinical evaluation 2
• In cases of high clinical suspicion, specific antibody testing should be performed regardless of screening test results 1

Laboratory Reporting Considerations

• Laboratories should specify the methods used for detecting antibodies 1
• For ANA, both pattern and titer should be reported 1
• Results for specific antibodies should be reported separately, including negative results 1