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What is the adrenal washout percent?

Enter the unenhanced, enhanced, and 15-minute delayed CT values of an adrenal mass to get its absolute and relative washout. For information only. This is not medical advice or a diagnosis. Do not use it to make treatment decisions without a clinician. No licensed clinician has reviewed this page.

Your numbers

Absolute washout (%)
83.3

The absolute washout is 83.3% (60% or more: in the adenoma range) and the relative washout is 62.5% (40% or more: in the adenoma range).

Relative washout (%)
62.5
Absolute washout
60% or more: in the adenoma range
Relative washout
40% or more: in the adenoma range
Unenhanced
Over 10 HU: washout decides

Absolute washout (%): 83.3. The absolute washout is 83.3% (60% or more: in the adenoma range) and the relative washout is 62.5% (40% or more: in the adenoma range).

This calculator gives general information only. It is not medical advice and does not replace a doctor or other health care provider. Talk with a professional about your results. Terms of use

How to calculate

Works out the absolute and relative contrast washout of an adrenal mass from unenhanced, enhanced, and delayed CT attenuation, and compares them with the published adenoma thresholds.

Example with the default inputs (Unenhanced (HU) 20, Enhanced (HU) 80, Delayed (HU) 30): The absolute washout is 83.3% (60% or more: in the adenoma range) and the relative washout is 62.5% (40% or more: in the adenoma range).

Method: Absolute washout = (enhanced − delayed) ÷ (enhanced − unenhanced) × 100. Relative washout = (enhanced − delayed) ÷ enhanced × 100. Adenoma range: absolute 60% or more, relative 40% or more, or unenhanced 10 HU or less.

  • The three values are region-of-interest means of the same mass, in Hounsfield units, from an adrenal protocol CT with a 15-minute delay.
  • Each washout is rounded once to 1 decimal, halves away from zero, and the shown value is compared with its threshold.

Machine-readable copies: Markdown, JSON.

Worked examples

Each example is checked against the calculator on every build.

  1. Unenhanced (HU) 20, Enhanced (HU) 80, Delayed (HU) 30 gives Absolute washout (%) 83.3, Relative washout (%) 62.5, Absolute washout 60% or more: in the adenoma range, Relative washout 40% or more: in the adenoma range, Unenhanced Over 10 HU: washout decides.Source: Caoili 2002 formulas: 50 ÷ 60 × 100 = 83.33
  2. Unenhanced (HU) 30, Enhanced (HU) 100, Delayed (HU) 75 gives Absolute washout (%) 35.7, Relative washout (%) 25, Absolute washout Under 60%: not in the adenoma range, Relative washout Under 40%: not in the adenoma range.
  3. Unenhanced (HU) -5, Enhanced (HU) 60, Delayed (HU) 20 gives Absolute washout (%) 61.5, Relative washout (%) 66.7, Unenhanced 10 HU or less: in the lipid-rich adenoma range.
  4. Unenhanced (HU) 35, Enhanced (HU) 90, Delayed (HU) 60 gives Absolute washout (%) 54.5, Relative washout (%) 33.3.
  5. Unenhanced (HU) 30, Enhanced (HU) 80, Delayed (HU) 90 gives Absolute washout (%) -20, Relative washout (%) -12.5, Absolute washout Under 60%: not in the adenoma range.

Medical disclaimer

This calculator is for information and education only. It is not medical advice, and its result is not a diagnosis. Do not use it to start, stop, or change a treatment without a clinician who knows your health history. No licensed clinician has reviewed this page. This site's editors checked the formulas and worked examples against published sources. If you think you have a medical emergency, call your local emergency number.

When this does not apply. The thresholds come from adults with adrenal masses scanned with an adrenal CT protocol: unenhanced, portal venous (about 60 seconds), and 15-minute delayed phases. Scans with another delay time give other washout values. Some tumors that are not adenomas, such as hypervascular metastases, can also wash out fast (Tay 2026).

How it works

Let U be the unenhanced value, E the enhanced (portal venous) value, and D the delayed value, all in HU.

  1. Absolute washout (%) = (E − D) ÷ (E − U) × 100.
  2. Relative washout (%) = (E − D) ÷ E × 100.
  3. No answer when E is not above U (no enhancement), when E is 0 HU or less, or when the enhancement is so small that a washout would be too large to show as a number.
  4. Each washout is worked from the exact typed values and rounded once to 1 decimal, halves away from zero. A negative result is shown with a minus sign.
  5. Readings: absolute washout 60% or more, relative washout 40% or more, and unenhanced 10 HU or less are each in the adenoma range (Caoili 2002; Tay 2026). The comparison uses the shown, rounded washout.

Worked examples by hand

Page default. U 20, E 80, D 30. Absolute: (80 − 30) ÷ (80 − 20) × 100 = 50 ÷ 60 × 100 = 83.33, 83.3%. Relative: 50 ÷ 80 × 100 = 62.5%. Both in the adenoma range; U is over 10 HU.

Slow washout. U 30, E 100, D 75. Absolute 25 ÷ 70 × 100 = 35.7%; relative 25 ÷ 100 × 100 = 25.0%. Neither is in the adenoma range.

Fat in the mass. U −5, E 60, D 20. Absolute 40 ÷ 65 × 100 = 61.5%; relative 40 ÷ 60 × 100 = 66.7%. U is 10 HU or less.

Between. U 35, E 90, D 60. Absolute 30 ÷ 55 × 100 = 54.5%; relative 30 ÷ 90 × 100 = 33.3%.

Negative washout. U 30, E 80, D 90. Absolute (80 − 90) ÷ 50 × 100 = −20.0%; relative −10 ÷ 80 × 100 = −12.5%.

Other questions people ask

How is adrenal washout calculated?

Absolute washout = (enhanced − delayed) ÷ (enhanced − unenhanced) × 100. Relative washout = (enhanced − delayed) ÷ enhanced × 100. All three values are CT attenuations of the mass in Hounsfield units (HU).

What washout suggests an adrenal adenoma?

An absolute washout of 60% or more and a relative washout of 40% or more are the usual adenoma thresholds. With the 60% rule and an unenhanced cut-off of 10 HU, Caoili et al. (2002) characterized 98% of adenomas and 92% of other masses correctly.

Why does an unenhanced value of 10 HU or less matter?

Fat lowers the CT value. A mass of 10 HU or less before contrast is in the lipid-rich adenoma range, so Caoili et al. did not need a washout scan for it.

When do I use the relative washout?

When there is no unenhanced scan. Relative washout needs only the enhanced and delayed values.

Can the washout be negative?

Yes. If the delayed value is higher than the enhanced value, the mass keeps gaining contrast and the washout is below 0, which is not in the adenoma range.

Are the thresholds certain?

No. The 2023 European Society of Endocrinology guideline says the evidence for the 60% and 40% cut-offs in incidentally found masses is weak, and some tumors that are not adenomas also wash out fast (Tay 2026). A radiologist reads the washout with the size and look of the mass.