Performance of Anti-Carbamylated Protein Antibody Testing in the Routine Evaluation of Rheumatoid Arthritis from a...

Area of Science:

• Rheumatology
• Immunology
• Clinical Diagnostics

Background:

• Rheumatoid arthritis (RA) diagnosis often relies on anti-CCP and RF antibodies, but these are absent in ~20% of patients.
• Antibodies against carbamylated proteins (anti-CarP) are emerging as potential biomarkers for early RA detection.
• This study evaluated the clinical utility of anti-CarP in diagnosing RA and assessing disease severity.

Purpose of the Study:

• To assess the clinical performance of anti-CarP antibodies in established rheumatoid arthritis (RA).
• To correlate anti-CarP positivity with RA disease severity, including bone erosions and synovitis.
• To evaluate the combined diagnostic performance of anti-CarP with anti-CCP and RF antibodies.

Main Methods:

• A retrospective review of 331 subjects, including 136 RA-positive and 195 RA-negative patients, alongside 50 healthy controls.
• Sera were tested for anti-CCP, RF, and anti-CarP antibodies using standard serological methods.
• Clinical performance metrics (sensitivity, specificity) were calculated for anti-CarP, both alone and in combination with other markers. Correlation with erosions and synovitis was assessed.

Main Results:

• Anti-CarP demonstrated a sensitivity of 27% and specificity of 94% for established RA, lower sensitivity than anti-CCP (79%) and RF (85%).
• Specificity of anti-CarP (94%) was comparable to anti-CCP (93%) and superior to RF (69%).
• While anti-CarP positivity correlated with synovitis, no correlation was found with bone erosions. Combination testing increased specificity but reduced sensitivity.

Conclusions:

• Anti-CarP antibodies exhibit high specificity but low sensitivity for diagnosing established RA.
• The combination of anti-CarP with anti-CCP and RF does not enhance overall diagnostic performance.
• Anti-CarP may be valuable for diagnosing RA in anti-CCP negative patients and identifying those with active disease, particularly synovitis.