Introduction Fatigue is a common symptom in RA and used as an outcome measure in RA clinical trials. We studied a large academic clinical practice to estimate the minimally important difference (MID) for a fatigue visual analog scale using patient-reported anchors (fatigue, pain and overall health). Methods RA patients (N=307) had clinic visits at 2 time points at a median of 5.9 months apart. They completed fatigue visual analog scale (VAS; 0–10) and retrospective anchor items, “How would you describe your overall fatigue/pain/overall health since the last visit?” Much worsened, Somewhat worsened, Same, Somewhat better, or Much better. The fatigue anchor was used for primary analysis and the pain/ overall health anchors for sensitivity analyses. The minimally changed group was defined by those reporting they were somewhat better or somewhat worsened. Results The mean (SD) age was 59.4 (13.2) years, disease duration was 14.1 (11.5) years, and 83% of patients were women. The baseline mean (SD) HAQ-DI score was 0.84 (0.75). The baseline fatigue VAS score was 4.2 (2.9) and at follow up was 4.3 (2.8) (mean change of −0.07 [2.5], p=NS). The fatigue change score (0–10 scale) for somewhat better and somewhat worsened for fatigue anchor averaged −1.12 and 1.26, respectively. Using pain anchor, the fatigue changed score for somewhat better and somewhat worsened averaged −0.87 and 1.13 and using global anchor, the fatigue changed score for somewhat better and somewhat worsened averaged −0.82 and 1.17, respectively. Effect size (ES) estimates using 3 anchors were small for somewhat better (range: 0.27 to 0.39) and somewhat worsened (range: 0.40 to 0.44) groups but larger than the no-change group (range: 0.03 to 0.08). Conclusions The MID for fatigue VAS is between −0.82 to −1.12 for improvement and 1.13 to 1.26 for worsening on 0–10 scale in a large RA clinical practice and similar to that seen in RA clinical trials. This information can aid in interpreting fatigue VAS in day-to-day care in clinical practice.

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