Association between social adaptability index and survival of patients with chronic kidney disease

Background. While individual socioeconomic factors have been associated with clinical outcome, a composite index has not been developed. In this project, we tested the hypothesis that Social Adaptability Index (SAI) based on employment, education, income, marital status and substance abuse is associated with survival in chronic kidney disease (CKD) patients. Methods. This is a retrospective cohort study of patients with CKD stage 2 or greater. We used the Third National Health and Nutrition Examination Survey (NHANES III) cohort data between 1988 and 1994 including those 18 years or older. Our primary variable of interest is SAI. Each component of SAI (employment status, education, marital status, and substance abuse) has been graded on the scale of 0-3, income has been graded on the scale 0-1. Age, sex, race, diabetes, co-morbidity index, body mass index (BMI), geographic location, haemoglobin, serum creatinine, serum albumin, serum cholesterol and Hba1c were used as covariates in multivariate analysis. The outcome of the study is patient's mortality. The time to death was calculated as time between the first interview by NHANES and death. Results. We analysed 13 400 subjects with mean age of 50.6 +/- 20-53.6% males, 44.4% white, 29.7% African American and 22.1% Mexican American-with 8.5% having diabetes, with an average number of co-morbid conditions of 2.7 +/- 1.1. Lower SAI is associated with greater stage of CKD. Higher SAI was associated with decreased mortality [hazard ratio (HR) 0.88, P < 0.001, 95% confidence interval (CI) 0.86-0.89]. When SAI quintiles were analysed, we demonstrated a 'dose-dependent' association between SAI and survival. Subgroup analysis showed that this association of SAI and survival was present in all studied subgroups. The limitations of the study include retrospective design, potential misreporting and misclassification, and reverse causality. Conclusion. Wedemonstrated that SAI has a strong and clinically significant association with mortality in CKD patients.