Objective: Evaluation of the individual relationship between C-reactive protein (CRP) production or erythrocyte sedimentation rate (ESR) and progression of radiologic damage in early rheumatoid arthritis (RA), to improve the predictive value of monitoring the acute phase response.
Methods: The relationship was modeled mathematically using adjustments for discontinuity in the radiographic scoring system and for clustering in the occurrence of score points in the initial phase. The model was evaluated in a prospective study of 149 patients with early RA, monthly CRP assays, and 6-monthly Sharp scores of radiographs of the hands and feet.
Results: Time integrated CRP values correlated closely with radiologic progression in each patient, but there was considerable variation between individuals with similar radiographic scores. The theoretical model accommodated these results, and based on CRP measurements and radiographic scores over 6 months, it provided a k value for each patient that reflected the individual relationship between CRP and radiologic damage. Using this k value combined with actual CRP levels over 3 and 6 years, the model accurately predicted the extent of radiologic progression that was actually observed at these times. Best results were obtained using estimation of the k value from 6 or 12 month observational data. The model has been incorporated into a software program for routine clinical use that indicates the levels to which CRP should fall to prevent further joint damage. Similar results were obtained for ESR.
Conclusion: A model has been established defining the individual relationship between time integrated CRP and ESR values, reflecting rheumatoid disease activity, and progression of radiologic damage. It accurately prediets outcome from 6 months after presentation and can be used as a practical decision support system.