Immunocompromised Status Definition in Observational Studies Using Electronic Health Records: A Scoping Review and a Proposal for a Phenotype Identification Algorithm

Immunocompromised individuals have weakened immune systems due to a congenital condition, an illness acquired later in life, or certain medical treatments. Some people might be immunocompromised only for a short period of time, and the variability of symptoms and diagnoses can vary widely. Hence, the identification of immunocompromised individuals in electronic healthcare records (EHRs) poses several challenges. We reviewed published studies to understand how other researchers have previously identified immunocompromised patients in EHR to conduct pharmacoepidemiologic studies. We grouped medical conditions and medications into seven categories: genetic conditions, infections, cancer and cancer treatments, organ and stem‐cell transplants, serious systemic illnesses, immunosuppressive drugs, and certain autoimmune diseases. In total, we reviewed 56 studies. The most frequently used diagnoses to identify immunocompromised individuals were HIV/AIDS and organ transplantation. Commonly used medications included methotrexate, corticosteroids, and other drugs that suppress the immune system. Building on this review and expert opinion, we developed an algorithm that combines diagnostic codes, medicines, and medical procedures to help identify immunocompromised populations in EHR data sources, facilitating the generation of more robust evidence in future studies.