Validation of functional activity index in patients with rheumatoid arthritis (RAS)

Abstract

Objective. To evaluate psychometric properties of Patient Activity Scale (PAS) index and possibility of its application for assessment of pt functional activity (PFA) and therapy efficacy in pts with rheumatoid arthritis (RA). Materia l and methods . Validity assessment was performed on 454 pts with definite RA,mainly female (85,2%) with mean age 51,3±11,3 years, mean disease duration was 9,1±8,5 years, 59,7% of pts were seropositive on rheumatoid factor, most pts had moderate or high inflammatory activity of the disease (95,6%), II or III radiological stage ( 44,7% and 27,8% respectively, II (53,5%) or III (31,8%) functional class. Constructive validity of the index was assessed by calculation of coefficients of correlation with “external criteria”. Sensitivity was assessed with ACR criteria in 285 pts after 6 months of standard therapy. Reliability (reproducibility and internal constancy) were assessed in 92 pts in 3 days after admission. Results. Assessment of PAS reliability with test-retest analysis did not reveal differences between first and repeat examination of pts whose state had not change after 3 days (mean scores 5,07±1,27 and 5,17±1,34 respectively, p=0,45). Intra-class Cronbach alpha coefficient was 0,95 (p<0,000001). Constructive validity assessment revealed moderate relationship of PFA with disease inflammatory activity measures: morning stiffness duration (r= 0,33, p<0,0000001), DAS 28 value (r=46, p<0,001), tender joint count (r=0,39, p<0,0000001), swollen joint count (r=0,28, p<0,0002) and weak relationship with ESR and radiological stage of the disease (r=0,17, p<0,00001). PAS correlation relationships with quality of life measures assessed on all SF-36 scales varied from -0,37 to -0,58. Index sensitivity to changes assessment showed that PAS change exceeding 0,22 corresponded to at least 20% health improvement according to ACR criteria. Conclusion . PAS is a reliable, valid and sensitive instrument of pt functional state self assessment and can be used for dynamic evaluation of pts state and treatment efficacy in outpatient practice