DAS28‐CRP Cutoffs for High Disease Activity and Remission Are Lower Than DAS28‐ESR in Rheumatoid Arthritis

OBJECTIVE: Guidelines do not specify how cutoffs for high disease activity differ between the Disease Activity Score 28‐joint count indices DAS28–erythrocyte sedimentation rate (ESR) and DAS28–C‐reactive protein (CRP). Studies that compare DAS28‐CRP and DAS28‐ESR depend on data from clinical trials, registries, or practices with multiple providers. Existing studies use data from patients who received immunosuppressive therapy. This study compared the DAS28‐ESR and DAS28‐CRP values from immunosuppressive treatment–naïve patients in a single physician practice. METHODS: A retrospective electronic medical chart review was conducted for new diagnoses of rheumatoid arthritis (RA; International Classification of Diseases [ICD]‐9 714), based on the American College of Rheumatology/European League against Rheumatology 2010 RA classification criteria. The number of patients with high disease activity (>5.1) was compared using ESR and CRP data to calculate the proportion of discordance. A receiver operator curve and Youden index was used to calculate the DAS28‐CRP high disease activity cutoff estimation that corresponds with DAS28‐ESR of more than 5.1. RESULTS: There were 171 patients included in this study. The baseline mean DAS28‐ESR was higher than the baseline mean DAS‐28 CRP: 5.1 ± 1.2 versus 4.1 ± 1.0 (P < 0.001); 48.5% of patients met criteria for high disease activity (score >5.1) compared with only 14.6% when measured by DAS28‐CRP. Discordance was 33.9%. κ coefficient was only .307. Receiver operator curve and Youden index analysis suggested that the cutoff point for high disease activity of DAS28‐CRP greater than 4.1, which corresponds to DAS28‐ESR greater than 5.1. Similarly, DAS28‐ESR posttreatment scores were significantly higher than DAS28‐CRP. When measured by DAS28‐ESR, patients in remission had higher scores as measured by DAS28‐ESR (1.81) than DAS28‐CRP (1.45). CONCLUSION: There is a difference between DAS28‐ESR and DAS28‐CRP, even when calculated for immunosuppressive treatment–naïve patients. DAS28‐CRP is significantly lower than DAS28‐ESR.