Impact of the use of self-perceived gender identity versus biological gender on the interpretation of laboratory tests: clinical and safety implications intransgender individuals

Laboratory medicine relies on sex-specific reference ranges for accurate interpretation. However, electronic records often register legal or self-identified gender, which may not reflect biological sex. This discordance can lead to misclassification of laboratory results and represents a potential patient-safety risk, particularly in transgender individuals. A retrospective cross-sectional study was conducted including 385 adults from a tertiary hospital. Thirty-eight sex-dependent laboratory parameters were analyzed. Each result was first interpreted using biological-sex reference ranges and then reassessed under the opposite sex to simulate potential misclassification. Significant differences occurred in 76.3% of parameters. In 23.3% of tests, discrepancies exceeded twenty percent, especially in sex hormones, renal function markers, and tumor markers. These divergences were clinically relevant when values fell within pathological ranges, indicating a meaningful risk of diagnostic error. Using gender identity alone for laboratory interpretation can result in diagnostic and therapeutic mistakes. Clinical practice should integrate biological sex, self-identified gender, and hormonal treatment status. Healthcare systems must adapt electronic health records and laboratory information systems to incorporate multiple sex-related fields to improve diagnostic accuracy and patient safety.