Validity of acute phase proteins as markers of disease activity

It has long been recognized that various rheumatic diseases, including rheumatoid arthritis (RA), are associated with a rise in concentration of acute phase proteins, particularly C-reactive protein (CRP) and serum amyloid A. The levels of these 2 proteins increase very rapidly over hours after the acute phase response is initiated. However, at present, only the measurement of CRP is widely available. Studies have shown that CRP is a better indicator of disease activity than erythrocyte sedimentation rate. CRP also appears to correlate with, and be predictive of, radiographic progression in RA. Although CRP has been shown to reflect disease activity and radiographic progression, there appears to be discordance between CRP response and drug therapy. With nonsteroidal anti-inflammatory drugs, there is essentially no change in the CRP response. However, CRP levels have been shown to decrease in patients who respond to disease modifying antirheumatic drugs. It is possible, therefore, that CRP could be used as an early predictor of response to therapy.