The erratic C-reactive protein: a novel outcome measure for longitudinal disease activity in rheumatoid arthritis

There is a relationship between both the magnitude and variability of C-reactive protein (CRP) levels and disease activity level in rheumatoid arthritis (RA). It seems that CRP levels remain low and stable in clinical remission then increase and become erratic in active disease. The purpose of this research was to determine if there is a difference in the variability of CRP levels over time in patients in clinical remission versus those with active disease.

Patients with a diagnosis of RA with a minimum of 3 CRP readings in the previous 12-month period were included at a single site. At each visit the patient was evaluated by an experienced rheumatologist to determine current disease activity - remission versus active disease. The primary outcome measure was the difference between the coefficient of variation of the CRP (CRP-COV) in patients in remission versus those with active disease.

272 patients were enrolled into the study. The mean CRP and CRP-COV was significantly smaller for patients in clinical remission versus active disease, for patients in CDAI remission (<2.6), and for those who did not require a change in treatment. Smokers, on average, had higher mean CRP readings regardless of clinical status.

We have identified a new clinical outcome measure of disease activity in RA that captures longitudinal variability in disease activity and identifies those patients with clinically active disease despite a "normal" CRP level due to the higher variability of CRP if not in remission.