Background: The Disease Activity Score (DAS-28) is the most widely used composite index of disease activity in rheumatoid arthritis (RA). Serial measurements of the DAS-28 are strong predictors of physical disability and radiological progression, and can sensitively discriminate between high and low disease activity. Several guidelines recommend the routine use of the DAS-28 to monitor the burden of disease and the response to treatment including biologic agents. In practice, clinicians may be reluctant to calculate the DAS-28 without a same day ESR, leading to unnecessary delay in adjusting intervention.

Objectives: The aim of this prospective cohort study was to assess whether ESR blood samples taken prior to the clinic appointment were adequate to accurately assess disease activity using the DAS-28.

Methods: 73 RA patients attending the rheumatology outpatient clinic at our institution were randomly selected and assessed at baseline. Mean age of participants was 61.8 years (range 20-85) with mean disease duration of 12.0 years (range 0.1-40). An ESR was obtained on the day of the appointment. The DAS-28 was calculated using this ESR which was then compared with the DAS-28 using an ESR taken prior to the clinic review (up to 6 months prior).

Results: Using the same day ESR versus pre-recorded ESR (range 6-190 days, mean interval 47days) to calculate the DAS-28 showed that the mean difference in DAS-28 was insignificant (-0.088, CI -0.158 to -0.018, p=0.01). The results were valid in all three disease categories of mild (DAS-28 2.6 to 3.2), moderate (DAS-28 >3.2-5.1) and severe (DAS-28 >5.1). Although most historical ESR values had been recorded within 2 months, even using multiple historical ESR measures from the same patients (N=151) over a period of up to six months still showed that the mean difference in DAS-28 remains very similar irrespective of time interval between the two ESR samples.

Conclusions: Our results indicate that in clinical practice changes in the DAS-28 due to a previous ESR are minimal. The difference in ESR values over a period of up to three months has no clinically significant contribution to variations in the DAS-28. A decision to adjust treatment therefore, may be confidently made using the most recent ESR for calculating DAS-28.

Disclosure of Interest: S. Brode: None Declared, M. Nisar: None Declared, A. Östör Consultant for: Roche, Chugai, Schering-Plough/MSD, Abbott, Wyeth, BMS, GSK, MerckSorono and UCB