BACKGROUND: Pre-analytical errors necessitate specimen rejection and negatively affect patient safety. Our purpose was to investigate the factors leading to specimen rejection and its impact. METHODS: Specimen rejections in a clinical chemistry laboratory during a 1-year period were reviewed retrospectively and analyzed for frequency, cause, circumstances, and impact. RESULTS: Of the 837,862 specimens received, 2178 (0.26%) were rejected. The most common reasons for specimen rejection were contamination (n=764, 35.1%), inappropriate collection container/tube (n=330, 15.2%), quantity not sufficient (QNS) (n=329, 15.1%), labeling errors (n=321, 14.7%), hemolyzed specimen (n=205, 9.4%), and clotted specimen (n=203, 9.3%). The analytes most often affected were glucose (n=192, 8.8%); calcium (n=152, 7.0%), magnesium (n=148, 6.8%), potassium (n=137, 6.3%), creatinine (n=100, 4.6%), and blood urea nitrogen (n=97, 4.4%). Outpatient service and blood draw by phlebotomists were associated with low rejection rates (536/493,501 or 0.11% and 368/586,503 or 0.06%, respectively). Recollection due to specimen rejection increased the turnaround time by an average of 108min. The total cost for the recollection was around $43,210 USD with an average cost around $21.9 USD. CONCLUSIONS: The factors associated with rejection are remediable by improved training and quality assurance measures. Policies and procedures specific to specimen collection, transportation, and preparation should be strictly followed.