Rust, Thomas J

ABSTRACT Background Cytomegalovirus (CMV) infection is among the most common infections after solid organ transplantation and leads to high rates of morbidity and mortality. With the proliferation of large, claims‐based datasets, there is a need to assess the validity of ICD‐10‐CM codes in identifying CMV infection. Methods We conducted a retrospective cohort study of solid organ transplant recipients (SOTRs) from a regional health system who underwent first transplantation between January 1, 2016, and June 30, 2025, had at least 30 days of post‐transplant follow‐up, and had known donor/recipient CMV serostatus. We performed cross‐sectional and time‐to‐event analyses comparing the test performance of B25 ICD‐10‐CM codes in identifying CMV infection, clinically significant CMV infection (csCMVi), CMV disease, and CMV DNA reaching various thresholds. Results Of 8169 SOTRs, 3084 (37.8%) had B25 coded during follow‐up. In addition, 4287 (52.5%) developed CMV infection, 2356 (28.8%) csCMVi, 297 (3.6%) CMV disease, and 1669 (20.4%) CMV DNA ≥ 1000 IU/mL. B25 codes were most specific to any CMV infection (88.5%), most sensitive to CMV DNA ≥ 100 000 IU/mL (98.2%), and csCMVi had the highest Youden's Index (0.651; sensitivity 84.1%, specificity 81.0%). Multivariable Cox regression provided similar results but with variations in effect measure between ICD‐10‐CM codes and clinical CMV definitions. Conclusions ICD‐10‐CM codes showed modest performance in identifying CMV infection, most closely resembling csCMVi. ICD‐10‐CM codes poorly reflect CMV severity, however, and may overestimate CMV infection by some clinical definitions. These limitations should be considered when using CMV diagnosis codes for claims‐based studies of SOTRs.