Physician explanation of Z-coded homelessness in medicaid claims

The International Classification of Diseases, 10th Revision (ICD-10) introduced a set of social determinants of health (SDOH) codes including Z59.0, indicating homelessness. Z codes are not widely used, and it is not clear how Z59.0 is used to document homelessness. The goal of this study was to examine patterns of Z59.0 within a linked administrative data set and explore physician explanations for coding prevalence. This study used sequential explanatory mixed methods, first examining claims data from New Jersey Medicaid linked to Homeless Management Information System (HMIS) data for adults aged 18 and older in 19 in 21 counties from 2014 to 2016 (n = 724,463). The rate and patterns of Z59.0 coding was compared to HMIS-recorded homeless service use. Then we conducted semi-structured interviews with 18 physicians at high-coding hospitals analyzed via thematic analysis. Only 1.1% of inpatient and ED claims were Z-coded. Claims for male individuals who were age 43-59, Non-Hispanic/White, enrolled via Medicaid expansion, of higher health burden, in the inpatient setting, or chronically homeless were more frequently Z-coded; this was consistent with physician expectations. Physicians were surprised by the frequency Z-coding of claims for individuals who were Non-Hispanic/White and could not give clear explanations as to why some hospitals had higher Z code prevalence. They suggested that individuals who had a Z code without known homeless service use were experiencing homelessness. This study suggests Z-coding for homelessness identifies individuals not using formal homeless services and may be useful to support provider efforts to address housing as a health-related social need.