The Short Form 36 Health Survey (SF-36) is a popular health-related quality of life (HrQoL) tool. However, few studies have assessed its psychometric properties in patients with spondyloarthritis (SpA). We therefore aimed to assess the reliability and validity of the SF-36 in patients with SpA in Singapore. Cross-sectional data from a registry of 196 SpA patients recruited from a dedicated tertiary referral clinic in Singapore from 2011 to 2014 was used. Analyses were guided by the COnsensus-based Standards for the selection of health Measurement INstruments framework. Internal consistency reliability was assessed using Cronbach's alpha. Construct validity was assessed through 33 a priori hypotheses by correlations of the eight subscales and two summary scores of SF-36 with other health outcomes. Known-group construct validity was assessed by comparison of the means of the subscales and summary scores of the SF-36 of SpA patients and the general population of Singapore using student's t tests. Among 196 patients (155 males (79.0 %), median (range) age: 36 (17-70), 166 Chinese (84.6 %)), SF-36 scales showed high internal consistency ranging from 0.88 to 0.90. Convergent construct validity was supported as shown by fulfillment of all hypotheses. Divergent construct validity was supported, as SF-36 MCS was not associated with PGA, pain and HAQ. Known-group construct validity showed SpA patients had lower scores of 3.8-12.5 when compared to the general population at p < 0.001. This study supports the SF-36 as a valid and reliable measure of HrQoL for use in patients with SpA at a single time point.

To determine if obesity is associated with poorer patient-reported outcomes (PROs) in patients with axial spondyloarthritis (axSpA), we conducted a cross-sectional study using data of the PRESPOND registry from a tertiary referral center in Singapore between 2011 and 2015. Demographics, clinical, and PRO variables were collected. Patients were divided into three categories: normal (BMI < 23 kg/m), overweight (23 kg/m ≤ BMI < 27.5 kg/m) and obese (BMI ≥ 27.5 kg/m), using Asian BMI classification. The dependent variables are Pain score, Bath Ankylosing Spondylitis Patient Global Score (BAS-G), Bath Ankylosing Spondylitis Disease Activity Index (BASDAI), Bath Ankylosing Spondylitis Functional Index (BASFI), Health Assessment Questionnaire (HAQ), and Medical Outcomes Study Short Form 36 version 2 (SF-36). Multivariate regression analyses were performed with these dependent variables and obesity categories, adjusting for confounders. Among 194 patients with axSpA, 32% are overweight while 22% are obese. We found that obese patients had significant poorer pain (β: 11.87, 95%CI 2.13, 21.60) and BAS-G scores (β: 10.18, 95%CI 1.59, 18.76) when compared to normal BMI patients. However, obesity was not associated with BASDAI (β 0.50, 95%CI -0.22, 1.22), BASFI (β 0.08, 95%CI -0.66, 0.81), HAQ (β -0.07, 95%CI -0.21, 0.06), physical component summary (β -0.02, 95%CI -4.47, 4.44), and mental component summary (β -2.85, 95%CI -7.57, 1.88) of SF-36. Obesity was associated with pain score and BAS-G but not with BASDAI, BASFI, HAQ, and SF-36. Further study is needed to examine the causal relationship between obesity and poorer PROs.

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BackgroundTo cross-culturally adapt and validate the Singapore Chinese and Singapore English versions of the Ankylosing Spondylitis Quality of Life (ASQoL) scales.MethodsTranslation of the ASQoL into Singapore Chinese and English was performed by professional and lay translation panels. Field-testing for face and content validity was performed by interviewing ten Chinese speaking and ten English speaking axial spondyloarthritis (AxSpA) patients. AxSpA patients (either Chinese or English speaking) were invited to take part in validation surveys. The Health Assessment Questionnaire (HAQ), Short Form Health Survey (SF-36), Bath Indices, and other measures of disease activity were used as comparator scales for convergent validity. A separate sample of AxSpA patients were invited to participate in a test-retest postal study, with 2 weeks between administrations.ResultsThe cross-sectional study included 183 patients (77% males, 82% English speaking), with a mean (SD) age of 39.4 (13.7) years. The ASQoL had excellent internal consistency (Cronbach’s alpha = 0.88), and correlated moderately with all the comparator scales. The ASQoL was able to distinguish between patients grouped by disease activity and perceived general health. The ASQoL fulfilled the Rasch model analysis for fit, reliability and unidimensionality requirements. No significant differential item functioning was noted for gender, age below or above 50 years, and language of administration. Test–retest reliability was good (r = 0.81).ConclusionsThe ASQoL was adapted into Singapore Chinese and English language versions, and shown to be culturally relevant, valid and reliable when used with combined samples of AxSpA patients who speak either Chinese or English.