Adrenal washout calculator
Enter the attenuation from each CT phase to get absolute and relative washout, then copy the summary.
For educational purposes only. This is not medical advice and does not replace clinical judgment. Check every result against the source guideline.
Leave empty if there is no unenhanced phase. You still get relative washout if enhanced attenuation is above 0 HU.
Portal venous phase, about 60 to 75 seconds after contrast.
15 minutes after contrast.
Enter the enhanced and delayed attenuation to see the washout.
The calculator runs in your browser, and the numbers you enter are never sent anywhere. Measure each phase with a matched, representative region of interest. Washout says nothing about hormonal function and does not override suspicious morphology, growth, size or a history of cancer.
The formulas
- Absolute washout
- (enhanced - delayed) / (enhanced - unenhanced) x 100
- Relative washout
- (enhanced - delayed) / enhanced x 100
Read this before you rely on washout
This calculator gives you the arithmetic. It does not say whether a lesion is an adenoma, because the evidence no longer supports reading that from washout alone.
A 2025 review concluded that washout CT should stop being used to assess true adrenal incidentalomas. It cites a study of 142 lesions above 10 HU in which 40 of 93 benign lesions (43 percent) failed the absolute washout criterion, and 11 of 49 malignant or potentially malignant lesions (22 percent) met it. That misclassified 51 of 142 lesions (36 percent). In a separate series of metastases from renal cell and hepatocellular carcinoma, the study abstract reports that washout criteria classified 18 of 19 (95 percent) as adenomas for one observer and 17 of 19 for the other.
The same review proposes raising the unenhanced threshold from 10 HU to 20 HU for lesions under 4 cm. That proposal, and the similar position in Radiology Assistant, applies only to homogeneous, true incidentalomas: no current or prior cancer elsewhere and no suspected adrenal disease, with endocrine assessment. It does not apply to a patient with a cancer history. It is the authors' proposal, not a consensus, so use the guideline your department follows.
- Washed up: the end of an era for adrenal incidentaloma CT (Seow et al, 2025)
- Adrenal washout CT in 142 lesions (Schloetelburg et al)
- Washout in renal cell and hepatocellular metastases (Choi et al, Radiology 2013)
- Characterization of adrenal lesions, update (Radiology Assistant)
- ACR Appropriateness Criteria: Adrenal Mass Evaluation
Common questions
- How do you calculate absolute adrenal washout?
- Subtract the delayed attenuation from the enhanced attenuation, divide by the enhanced attenuation minus the unenhanced attenuation, and multiply by 100. A lesion at 20 HU unenhanced, 100 HU enhanced and 40 HU delayed has an absolute washout of 75 percent.
- How do you calculate relative adrenal washout?
- Subtract the delayed attenuation from the enhanced attenuation, divide by the enhanced attenuation, and multiply by 100. It needs no unenhanced phase. A lesion at 100 HU enhanced and 40 HU delayed has a relative washout of 60 percent.
- What are the usual washout thresholds?
- Absolute washout of 60 percent and relative washout of 40 percent, using a 15 minute delayed phase. Sources write these both as "above" and as "at least" the figure. This calculator counts a value exactly on the line as meeting it.
- Is adrenal washout CT still recommended?
- It is contested. The 2017 ACR white paper includes washout in its algorithm for selected indeterminate lesions, depending on size and history. A 2025 review concluded it should stop being used for true adrenal incidentalomas, and Radiology Assistant takes the same view. Follow your department's protocol.
- Which lesions can mimic an adenoma on washout?
- Pheochromocytomas and hypervascular metastases, such as those from renal cell and hepatocellular carcinoma. Adrenocortical carcinoma can also show similar percentages. The calculator can't separate these, so it reports the numbers and makes no diagnosis.
- Why does the calculator show no absolute washout?
- If the unenhanced field is empty, you get relative washout only, as long as enhanced attenuation is above 0 HU. If enhanced attenuation is less than 10 HU above unenhanced, you get neither figure, because a percentage of so small a rise is noise. The calculator calls the lesion non-enhancing only if the delayed phase is also within 10 HU of unenhanced, in line with the ACR. You also get neither figure if delayed attenuation is below unenhanced, which points to a phase or measurement problem.
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