Association Between Socioeconomic Status and Comorbidities Among Patients With Rheumatoid Arthritis

Results of a Nationwide Cross-Sectional Survey

Anna Shin; Seunghwan Shin; Ji Hyoun Kim; You-Jung Ha; Yun Jong Lee; Yeong Wook Song; Eun Ha Kang


Rheumatology. 2019;58(9):1617-1622. 

In This Article


Data Source and Study Population

KNHANES is an annual survey to investigate the health and nutritional status of the Korean population aged ≥1 year.[8] Face-to-face health interviews and medical examinations are core components of the KNHANES, conducted by trained professional investigators. Using established questionnaires, the health interview collects information on SES (income, education, area of residence), co-morbidities, mental status, health-related behaviors and healthcare utilization. Medical examinations measure anthropometric and biochemical (haemoglobin, fasting glucose, cholesterol and triglyceride levels) profiles and blood pressure. We used 2007–2015 KNHANES in this study (unweighted prevalence of missing data was: ≤1.5% for SES, 0% for comorbidities and ≤5% for medical examination results). This study was approved by the institutional review board of Seoul National University Bundang hospital. The study was conducted in accordance with the Declaration of Helsinki and International Conference on Harmonization good clinical practices. The protocols were reviewed and approved by the institutional review board of Seoul National University Bundang Hospital (X-1809-493-901). All patients provided written informed consent before undergoing the survey.

RA and Other Comorbidity Status

The presence of RA or comorbid conditions was based on a physician-made diagnosis: patients who answered yes to 'was your RA diagnosed by a physician' were classified as having RA.[8] The presence of comorbidities (Supplementary Table S1, available at Rheumatology online) was defined in the same manner. Mental status was assessed by an established questionnaire and recorded in terms of three items: high stress, depressive mood and suicide ideation (Supplementary Table S2, available at Rheumatology online).[8]

Definitions of Socio-economic Status Levels

The upper two quartiles of weighted household income were categorized as high, whereas the bottom two were low. Graduation from high school or higher education was defined as high education vs middle school or lower as low. Area of residence was classified as urban vs rural according to the administrative district.

Health-related Behavior and Healthcare Service use

Participants were asked to select one or more exercise patterns from vigorous, moderate and low intensity (Supplementary Table S2, available at Rheumatology online). Alcohol consumption and smoking habits were recorded. Patients' ability to access healthcare institutions when in need, hospitalization frequency during the past year and the frequency of outpatient clinic visits within two months from the interview were examined.[8]

Statistical Analyses

The weighted univariate comparison between high and low SES was done using χ 2tests, or Student-t tests. Logistic regression analysis was performed to estimate the age-adjusted odds ratio (OR) and 95% confidence interval (CI) for comorbidity prevalence. Statistical analyses were performed using SAS version 9.4 considering two-sided P-values of <0.05 as significant.