In a study, it was demonstrated that the MIC (minimal important change) for PAS-II was approximately 0.5. Among participants with moderate to high PAS-II, the MCII was 1.1. Among participants with low disease activity, the MCIW was found to be 1.1.

This large patient registry aimed to define the MCII (Minimal Clinically Important Improvement) and MCIW (Minimal Clinically Important Worsening) for the PAS-II (range 0-10), a recommended well-validated patient-reported outcome measuring the activity of rheumatoid arthritis disease.

Data from Forward, The National Databank for Rheumatic Diseases from four 6-month data

collection periods were used. To estimate MCII and MCIW, both anchor-based and distribution-based methods were used. Anchor-based analyses used comparisons of pain and general health compared to six months ago. Distribution-based analyses used 0.5 and 0.35 SD (standard deviations).

The analyses were stratified based on the PAS-II score (above/below 3.7). It was hypothesized that the MCII and MCIW would depend on the baseline score. To determine construct validity, the odds of achieving the MCII in patients receiving novel therapies were examined.

In the overall sample, the MCIW was 0.50 and 0.55 for pain and general health-related questions respectively. The MCII was defined as 0.39 to 0.45, respectively as shown in Table 1:

Among patients with low disease activity (PASII3.7),  the MCIW for pain and health-related anchor questions were 1.09 and 1.11, respectively. Among patients with high disease activity (PAS-II >3.7), the MCII for pain and health-related anchor questions were 1.15 and 1.02, respectively as shown in Table 2:

Distribution-based methods resulted in a minimal clinically important change of 1.08 and 0.76, for 0.5 SD and 0.35 SD respectively as depicted in Table 3:

A fair to excellent agreement with clinically significant differences in assessments of pain and disability was witnessed. Patients initiating new treatments for RA had 30% greater odds of attaining the MCII. Thus, the characterization of clinically meaningful changes in disease activity is crucial for clinical research studies and clinical settings where this disease assessment is utilized.