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To retrospectively evaluate the diagnostic values of absolute percentage washout ratio (APW) and relative percentage washout ratio (RPW) obtained from a short time delay triphasic enhanced CT in distinguishing adenomas from non-adenomas. The study population consisted of 116 patients (58 males and 58 females; mean age, 52 years; age range, 23–89 years) with 116 adrenal masses from 2010 to 2016. Absolute attenuation values in each phase of CT were measured, and then the APW and RPW were calculated. The APW and RPW receiver operating characteristic (ROC) analysis was performed to evaluate the strength of the tests. Sensitivity, specificity, and accuracy were calculated for APW and RPW. Significant differences were observed in APW and RPW values between the adenoma and non-adenoma groups (p < 0.001). Areas under the ROC curve were 0.822 (95% confidence interval: 0.730, 0.914) and 0.913 (95% confidence interval: 0.851, 0.975) for the APW and RPW tests, respectively. The RPW (≥30%) criterion showed the best accuracy (86%), with 85% sensitivity and 90% specificity, followed by the APW (≥32%) criterion, with 81% accuracy, 85% sensitivity, and 69% specificity. The APW and RPW values from a short time delay triphasic enhanced CT were efficient and helpful in differentiating adenomas from non-adenomas, and could provide comparable diagnostic results to the previous reported longer delayed dedicated adrenal CT protocols. The washout ratio from a short time delay triphasic enhanced CT could help in differentiating adenomas from non-adenomas without the dedicated adrenal CT. [ABSTRACT FROM AUTHOR]