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Objective: To determine if anemia can be predicted on unenhanced computed tomography (CT) of the thorax., Methods: Hemoglobin and hematocrit levels were obtained within 24 hours of the unenhanced CT scan of the thorax of 200 patients. Anemia was defined as a hemoglobin level less than 140 g/L for men and less than 120 g/L for women. Regions of interest were placed on the left ventricular cavity, aorta and the interventricular septum if visualized. The attenuation of the interventricular septum and left ventricular cavity were correlated with the presence or absence of anemia., Results: When the interventricular septum was not visualized, for every 1 Hounsfield unit (HU) increase in left ventricular attenuation, hemoglobin increased by 0.435 g/L (SE = 0.253, p < 0.001). Failure to visualize the interventricular septum did not exclude the presence of anemia in either sex. When the interventricular septum was visualized, 100% of males and 89% of females met the criteria for the diagnosis of anemia. The prediction of anemia by visualization of the interventricular septum alone yielded a sensitivity of 75.4% and a specificity of 90.3%, with 80% of patients correctly predicted. The multiple regression analysis model yielded a sensitivity of 94.2% and a specificity of 67.7%, with 86% of patients correctly predicted., Conclusion: The diagnosis of anemia should be suggested whenever the interventricular septum is visualized on unenhanced CT.