Same-day or historical ESR for disease activity score measurement: does it matter?

Several guidelines recommended routine use of Disease Activity Score-28 (DAS28) to monitor disease and the response to treatment for rheumatoid arthritis (RA). In practice, it may be appropriate to use historical erythrocyte sedimentation rate (ESR) values in place of same-day ESR, thereby preventing unnecessary delay in adjusting intervention. We asked whether ESR blood samples taken up to 3 months prior to the clinic appointment were adequate to accurately assess RA disease activity using the DAS28. RA patients (N = 66) who met the inclusion criteria were assessed at baseline and ESR obtained on the day of review to calculate the DAS28 and compared with the DAS28 derived from the latest previous ESR (mean interval, 38.6 days; range, 6-99 days). Limits of agreement (LoA) were used to assess the agreement between the DAS28 pairs. The mean age of the participants was 61.5 years (range, 20-83 years), with mean disease duration of 11.0 years (range, 0.1-40 years). Comparing the DAS28 using same-day ESR versus pre-recorded historical ESR showed a small statistical difference (mean, -0.09; 95 %CI, -0.1602 to -0.017) in the DAS28 score. The calculated LoA (-0.66 and 0.48) demonstrated acceptable agreement between DAS28 pairs, with 7.6 % of patients residing outside the LoA, all of whom had a significant treatment change. Disease misclassification occurred in 9.1 % of patients who were close to disease activity boundaries. Our results indicate that differences in the DAS28 due to a previous or same-day ESR are unlikely to be clinically significant for RA patients with established disease. A decision to adjust treatment therefore may be confidently made for most patients using the most recent ESR for calculating the DAS28, provided there was no major change in treatment since the last ESR measurement.