Including Undocumented Immigrants in Health Research-A Narrative Review of Barriers, Effective Approaches, and Best Practices in the United States.

Background and Aims: Undocumented immigrants (UDIs) in the United States are an understudied population with unique health needs. Half are uninsured, with state-to-state variation. Creative methodologies have been used to approximate UDIs in health data by geography and scope. However, no review exists of UDI health coverage or methods used to study this population. We conducted a narrative review defining health coverage options by state and research methodologies for UDIs. Methods: We conducted a narrative review of the literature to answer two research objectives: (i) what health coverage is available to UDIs at the federal and state level, and (ii) what methodologies have been used by health services researchers to study UDI health. First, we reviewed Medicaid websites, gray literature, and legislative briefs to summarize federal and state-level health coverage for UDIs. We categorized states by care availability into three groups: "available," "limited," and "restricted." We then conducted a formal literature search on health research among UDIs for every state, using gray literature and articles from PubMed and Google Scholar. Data was extracted to describe study characteristics, data type, methods for approximating or identifying UDI data, and scope. Total number of health studies by state was grouped according to their care availability status. Results: UDI health coverage was determined for all 50 states and Washington, DC: three states and Washington, DC were considered "available," 28 were "limited," providing care to special UDI populations, and 19 were "restricted" with no coverage options. Thirty-seven articles on UDI health coverage were included in this study. Methodologies to study UDI patients were unstandardized. Most studies were single-center, retrospective, or qualitative. Creative methods were used to approximate UDI health data, including linking social services datasets and using Emergency Medicaid claims. Large-scale data set studies were rare, but California's restricted Medi-Cal demonstrated successful use of claims data for UDI research. Included research articles were categorized by state coverage and an average number of studies produced per state in that category: available ( Conclusions: From this narrative review on health coverage and health studies on UDI patients, we found variability in health coverage, unstandardized methods to approximate UDI patients, and creative and diverse methodologies to study UDI populations, with varied degrees of accessibility and accuracy for approximating this population. Understanding these approaches can better inform health researchers when studying the health of UDIs to apply these methodologies to their own contexts and research questions.