Diagnostic Errors in Clinical Laboratory Testing Process: Incidence and Impacts on Patient Safety—A 3-Year Voluntary Incident Report Analysis

Abstract Introduction Diagnostic errors in laboratory processes can compromise the accuracy of final diagnoses. Such errors represent a significant patient safety concern and are linked to adverse clinical outcomes. This study aimed to determine the frequency, types, and impacts of laboratory-related diagnostic errors on the final clinical diagnosis, patient harm, and organizational reputation in a large private hospital network in Thailand. Methods A retrospective study analyzed diagnostic errors in clinical laboratory testing processes at Bangkok Hospital Headquarters (BHQ), Thailand, over a three-year period (January 1, 2021—December 31, 2023). Data were retrieved from a voluntary incident reporting system covering domains such as clinical hematology, clinical chemistry, metabolic diagnostics, genetics, microbiology, hormonology, serology, and coagulation. Descriptive statistics were employed to classify errors by laboratory process, sub-process, and subtype, identify causal factors, and evaluated the clinical impacts. Results Out of 5,951,783 samples processed, 34,395 incidents were reported, of which 1,031 (2.9%) related to diagnostic errors. Errors predominantly occurred in the pre-analytical process (89.2%), followed by post-analytical (10.7%) and analytical process (0.1%). The most common error subtypes were incorrect test ordering (48.2%) and specimen collection (34.6%). Human factors accounted for 91.1% of errors, with technical and organizational factors contributing minimally. 90.6% of errors had no impact on final clinical diagnosis; 7.8% resulted in delayed diagnosis, 0.9% in missed diagnosis, and 0.7% in wrong diagnoses. Most errors (98%) caused no patient harm, 1.9% led to temporary harm, and one error affected organizational reputation. No sentinel events were reported. Discussion and Conclusion To strengthen diagnostic safety across healthcare systems, organizations should adopt comprehensive, system-level strategies that effectively address human-factor vulnerabilities and streamline laboratory workflows. Implementing evidence-based strategies could contribute to achieving higher diagnostic accuracy and advancing patient safety within clinical laboratory processes.