Which laboratory test is highly specific for RA?

Which laboratory test is highly specific for RA?

• A. Erythrocyte sedimentation rate
• B. C-reactive protein
• C. Cyclic citrullinated peptide antibody (anti-CCP)
• D. Rheumatoid factor

Answer: (C)

Antibodies to cyclic citrullinated peptides are highly specific for rheumatoid arthritis because they recognize citrullinated proteins, a modification strongly associated with RA that is rarely seen in other conditions. This gives anti-CCP testing a very high specificity, so a positive result greatly strengthens the likelihood of RA and helps distinguish it from other joint diseases. In contrast, markers like erythrocyte sedimentation rate or C-reactive protein reflect general inflammation and can be elevated in many conditions, not just RA. Rheumatoid factor is often present in RA but also appears in other diseases and in some healthy people, reducing its specificity. Therefore, anti-CCP is the best single test for confirming RA, though a negative result does not completely exclude the disease and must be interpreted alongside clinical features and other findings.

Antibodies to cyclic citrullinated peptides are highly specific for rheumatoid arthritis because they recognize citrullinated proteins, a modification strongly associated with RA that is rarely seen in other conditions. This gives anti-CCP testing a very high specificity, so a positive result greatly strengthens the likelihood of RA and helps distinguish it from other joint diseases. In contrast, markers like erythrocyte sedimentation rate or C-reactive protein reflect general inflammation and can be elevated in many conditions, not just RA. Rheumatoid factor is often present in RA but also appears in other diseases and in some healthy people, reducing its specificity. Therefore, anti-CCP is the best single test for confirming RA, though a negative result does not completely exclude the disease and must be interpreted alongside clinical features and other findings.