Identification of Cutpoints for Acceptable Health Status and Important Improvement in Patient-Reported Outcomes, in Rheumatoid Arthritis, Psoriatic Arthritis, and Ankylosing Spondylitis

Abstract

To identify cutpoints reflecting Patient Acceptable Symptom State (PASS) and Minimal Clinically Important Improvement (MCII) in patient-reported multi-attribute health status classification systems and health status measurements among patients with rheumatoid arthritis (RA), ankylosing spondylitis (AS), and psoriatic arthritis (PsA). We identified patients with RA, AS, and PsA from the Norwegian disease-modifying antirheumatic drug (DMARD) register (NOR-DMARD). The patients (n = 4225) had started with DMARD and responded to the PASS and MCII anchoring questions at the 3-month followup examination. Receiver operating characteristics (ROC) curves with 80% specificity and the 75th percentile approach were used to identify PASS and MCII cutpoints in the EuroQol-5 Dimensions (EQ-5D) and the Short-Form-6 Dimensions (SF-6D) indexes, but also in other patient-reported outcomes (joint pain and patient global visual analog scale and Modified Health Assessment Questionnaire). The PASS cutpoints estimated with 80% specificity were around 0.70 in EQ-5D in all diseases and around 0.65 in SF-6D. The cutpoints were around 0.65 and 0.60, respectively, when the 75th percentile approach was used. The MCII cutpoints assessed by 80% specificity varied from 0.10 to 0.19 in EQ-5D and from 0.07 to 0.10 in SF-6D. The cutpoints for PASS in EQ-5D and SF-6D indicate that PASS corresponds to a health-related quality of life that is far from perfect health. Somewhat different cutpoints were identified for both PASS and MCII with 80% specificity versus the 75th percentile method.