Preanalytical sample rejection patterns and quality indicators in the central laboratory of a tertiary university hospital: a retrospective analysis according to clinical department and patient subgroups

Aims: Preanalytical errors remain the leading source of laboratory testing errors and may compromise analytical reliability, delay clinical decision-making, increase healthcare costs, and adversely affect patient safety. Continuous monitoring of sample rejection patterns is essential for identifying institution-specific weaknesses and improving laboratory quality management systems. This study aimed to evaluate the causes of preanalytical sample rejection in a tertiary university hospital laboratory and to investigate rejection patterns according to clinical department category, patient admission status, and patient age group. Methods: This retrospective study included all rejected samples recorded in the Laboratory Information System between January 1 and June 30, 2025. Rejected specimens were classified according to rejection reason, sample tube type, clinical department category, patient admission status (inpatient/outpatient), and patient age group (adult/pediatric). Major rejection causes were grouped into five categories: insufficient sample volume, clotted sample, unanalyzable coagulation sample, hemolyzed sample, and other causes. Categorical variables were compared using the Chi-square test, with statistical significance defined as p<0.05. Results: A total of 4,598 rejected samples were analyzed. The most common rejection reasons were insufficient sample volume (44.2%), clotted samples (36.8%), unanalyzable coagulation samples (9.0%), and hemolyzed samples (4.7%). Significant differences in rejection patterns were observed among clinical department categories (χ²=332.861, p<0.001). Insufficient sample volume predominated in adult medical clinics (56.7%) and outpatient clinics (58.2%), whereas clotted samples were the leading rejection cause in adult intensive care units (41.5%), neonatal intensive care units (60.6%), and pediatric intensive care units (57.5%). Rejection patterns also differed significantly between inpatient and outpatient samples (χ²=45.041, p<0.001); outpatient specimens demonstrated higher proportions of insufficient sample volume (47.0%) and hemolyzed samples (7.5%), whereas clotted samples were more frequent among inpatients (38.5%). Furthermore, significant differences were observed between adult and pediatric patients (χ²=38.501, p<0.001), with insufficient sample volume predominating in adults (45.4%) and clotted samples in pediatric patients (48.4%). Conclusion: Preanalytical sample rejection patterns differ significantly according to clinical department characteristics, patient admission status, and patient age group. Incorporating subgroup-specific analyses into routine laboratory quality indicator monitoring may facilitate targeted quality improvement interventions, optimize specimen collection practices, and enhance patient safety and laboratory performance.