Background/Purpose:   To investigate the influence of age on the components of the 28-joint Disease Activity Score (DAS28)-C-reactive protein (CRP) in patients with rheumatoid arthritis (RA) and whether DAS28-CRP can be equally interpreted in all age groups.  

Methods: For RA subjects enrolled in the University of Pittsburgh Rheumatoid Arthritis Comparative Effectiveness Registry (RACER), a cross-sectional analysis was performed. The share was expressed as a proportion and calculated by dividing the formula the DAS28 by the entire DAS28 (CRP share = [0.36 x ln(CRP +1] / DAS28, Relative of the contribution of the patient reported measures (tender joint count [TJC] and patient global assessment [PtGA] in DAS28-CRP [DAS-P] = [0.56 x sqrt (TJC) + 0.014 x PtGA] / DAS28-CRP).  Share of CRP and patient reported components of the DAS28 (DAS-P) were analyzed and compared between 2 age groups (younger RA <60, older RA ¡Ã 60) using Mann-Whitney U test. Inflammatory disease burden in the joint was calculated by modified DAS28 (MDAS28 = 0.49 x ln(C-reactive protein (CRP)) + 0.15 x swollen joint count 28 (SJC) + 0.22 x physician global assessment (PhGA) +1). Multivariate analyses were used to design models best predicting the effect of age on CRP, the share of CRP, inflammation level calculated by MDAS28, DAS-P, and pain levels.

Results:   CRP and the share of CRP in DAS28-CRP were not influenced by age. MDAS28 did not increase significantly with age but was associated with disease duration and anti-tumor necrosis factor (TNF) therapy. Female gender had significantly higher DAS-P, while age was associated with lower DAS-P. Pain level had significant negative association with age (Table 1). In subjects with moderate inflammation (defined by MDAS28 score above 50 percentile, N=370), older RA subjects (age >= 60, N=189) had lower pain level, tender joint count (TJC), patient and physician global assessment, DAS28-CRP than younger subjects (age < 60, n=157) (Table 2). 

Conclusion:   CRP, CRP share, and MDAS28 were not associated with age. However, age played a role in how subjective components of DAS28-CRP and pain level are assessed and rated in patients with RA. Disease activity could be underestimated by DAS28-CRP in older RA patients with moderate to high grade inflammation from RA.