Objective: To systematically analyze the common causes leading to inaccurate coagulation test results and their respective impact levels on various parameters, providing a basis for laboratory quality control and clinical specimen collection. Methods: A retrospective analysis was performed on the data of 209 re-tested coagulation specimens. All specimens were divided into four groups according to the initial test results: coagulated blood, suspected heparin contamination, insufficient specimen volume, and elevated hematocrit. Seven coagulation indicators including PT, APTT, TT, FIB, FDP, AT-III, and D-D were collected before and after re-examination. The differences in the above indicators between initial and re-test results in each group were compared between groups. Results: Clotted blood specimens were primarily characterized by abnormally elevated FDP and D-D (median: 28.7 μg/mL and 15.5 μg/mL, respectively) and decreased FIB (median: 2.14 g/L). After re-testing, these values decreased (FDP and D-D median was 4.5 μg/mL and 2.2 μg/mL, respectively) or increased (FIB median: 3.31 g/L). Suspected heparin contamination most significantly affected PT, APTT, and TT, which shortened by 9.2 s, 46.4 s, and 19.6 s (median), respectively, after re-testing. Insufficient sample volume primarily caused prolongation of PT and APTT, which decreased by 6.6 s and 10.3 s (median), respectively, after re-testing. Elevated hematocrit can also cause prolongation of PT and APTT. After re-examination, their mean values decreased by 49.9 s and 27.6 s, respectively. Conclusion: Errors in coagulation tests caused by different specimen issues present characteristic changes. Blood clotting mainly affects FDP, D-D, and FIB, while suspected heparin contamination, insufficient specimen volume, and elevated hematocrit predominantly prolong PT and APTT. Therefore, qualified specimen quality is essential for the accuracy of coagulation testing. Meanwhile, establishing a standardized review and intervention process based on cause analysis in the clinical laboratory is critical to improving the quality of coagulation assays.