Background: Abdominal trauma, leading to intra-abdominal bleeding, is a life-threatening condition that might need emergency surgical intervention. Sonography and Computed Tomography (CT) are most commonly used to detect free intra-abdominal fluid. This study investigates the accuracy of CT to distinguish between ascites and intra-abdominal hemorrhage. Methods: Ascites were collected during a clinical routine. Three serial dilutions, mixing ascites with whole blood samples of the patient and with two blood group identical donors, were prepared. Laboratory-chemical analysis and radiological evaluation using CT with measurement of average Hounsfield Units (HU) were performed. Results: Between ascites and whole blood as well as between ascites and the 1:1-ratio-samples, HU values differed significantly (p < 0.001). All further dilutions showed HU values with no significant difference compared to ascites (p >= 0.42). Whole blood showed significantly higher HU values than ascites and every step of the serial dilutions (p < 0.001). Measured HU values were also dependent on time and the exact point of measurement in the micro reaction vessels. Conclusions: In patients suffering from blunt abdominal trauma with preexisting ascites, HU values in CT imaging are not valid enough to exclude an acute hemorrhage.