{
  "id": "adrenal-washout",
  "version": "9fff7e39d7e8",
  "status": "published",
  "name": "Adrenal Washout Calculator",
  "question": "What is the adrenal washout percent?",
  "summary": "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.",
  "category": "health",
  "subcategory": "clinical",
  "url": "https://www.acalculator.org/health/adrenal-washout-calculator",
  "markdown": "https://www.acalculator.org/health/adrenal-washout-calculator.md",
  "kind": "function",
  "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.",
  "assumptions": [
    "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."
  ],
  "inputs": {
    "$schema": "https://json-schema.org/draft/2020-12/schema",
    "type": "object",
    "properties": {
      "pre": {
        "title": "Unenhanced (HU)",
        "description": "Attenuation of the mass before contrast. In Hounsfield units (HU), -100 to 100.",
        "type": "number",
        "minimum": -100,
        "maximum": 100
      },
      "enh": {
        "title": "Enhanced (HU)",
        "description": "Attenuation in the portal venous phase, about 60 s after contrast. In Hounsfield units (HU), -100 to 400.",
        "type": "number",
        "minimum": -100,
        "maximum": 400
      },
      "del": {
        "title": "Delayed (HU)",
        "description": "Attenuation on the delayed scan, 15 minutes after contrast. In Hounsfield units (HU), -100 to 400.",
        "type": "number",
        "minimum": -100,
        "maximum": 400
      }
    }
  },
  "outputs": {
    "apw": {
      "label": "Absolute washout (%)",
      "description": "(Enhanced − delayed) ÷ (enhanced − unenhanced) × 100, to 1 decimal.",
      "format": "number"
    },
    "rpw": {
      "label": "Relative washout (%)",
      "description": "(Enhanced − delayed) ÷ enhanced × 100, to 1 decimal.",
      "format": "number"
    },
    "apwReading": {
      "label": "Absolute washout",
      "description": "Against the 60% threshold.",
      "format": "text"
    },
    "rpwReading": {
      "label": "Relative washout",
      "description": "Against the 40% threshold.",
      "format": "text"
    },
    "preReading": {
      "label": "Unenhanced",
      "description": "Against 10 HU.",
      "format": "text"
    }
  },
  "defaultAnswer": {
    "inputs": {
      "pre": 20,
      "enh": 80,
      "del": 30
    },
    "outputs": {
      "apw": 83.3,
      "rpw": 62.5,
      "apwReading": "60% or more: in the adenoma range",
      "rpwReading": "40% or more: in the adenoma range",
      "preReading": "Over 10 HU: washout decides"
    },
    "text": "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)."
  },
  "examples": [
    {
      "given": {
        "pre": 20,
        "enh": 80,
        "del": 30
      },
      "expect": {
        "apw": 83.3,
        "rpw": 62.5,
        "apwReading": "60% or more: in the adenoma range",
        "rpwReading": "40% or more: in the adenoma range",
        "preReading": "Over 10 HU: washout decides"
      },
      "source": "Caoili 2002 formulas: 50 ÷ 60 × 100 = 83.33; 50 ÷ 80 × 100 = 62.5 (hand calculation in content.mdx)"
    },
    {
      "given": {
        "pre": 30,
        "enh": 100,
        "del": 75
      },
      "expect": {
        "apw": 35.7,
        "rpw": 25,
        "apwReading": "Under 60%: not in the adenoma range",
        "rpwReading": "Under 40%: not in the adenoma range"
      },
      "source": "25 ÷ 70 × 100 = 35.71; 25 ÷ 100 × 100 = 25.0 (hand calculation in content.mdx)"
    },
    {
      "given": {
        "pre": -5,
        "enh": 60,
        "del": 20
      },
      "expect": {
        "apw": 61.5,
        "rpw": 66.7,
        "preReading": "10 HU or less: in the lipid-rich adenoma range"
      },
      "source": "40 ÷ 65 × 100 = 61.54; 40 ÷ 60 × 100 = 66.67 (hand calculation in content.mdx)"
    },
    {
      "given": {
        "pre": 35,
        "enh": 90,
        "del": 60
      },
      "expect": {
        "apw": 54.5,
        "rpw": 33.3
      },
      "source": "30 ÷ 55 × 100 = 54.55; 30 ÷ 90 × 100 = 33.33 (hand calculation)"
    },
    {
      "given": {
        "pre": 30,
        "enh": 80,
        "del": 90
      },
      "expect": {
        "apw": -20,
        "rpw": -12.5,
        "apwReading": "Under 60%: not in the adenoma range"
      },
      "source": "−10 ÷ 50 × 100 = −20.0; −10 ÷ 80 × 100 = −12.5 (hand calculation in content.mdx)"
    }
  ],
  "sources": [
    "Caoili EM, Korobkin M, Francis IR, et al. Adrenal masses: characterization with combined unenhanced and delayed enhanced CT. Radiology. 2002;222(3):629-633. https://doi.org/10.1148/radiol.2223010766 (retrieved 2026-10-05)",
    "Tay BHB, Sim JZT, Low G. Pitfalls of adrenal washout on CT in the adult population: a pictorial review. Diagnostics (Basel). 2026;16(6):920. https://doi.org/10.3390/diagnostics16060920 (open at https://pmc.ncbi.nlm.nih.gov/articles/PMC13025807/, retrieved 2026-10-05)",
    "Peña CS, Boland GW, Hahn PF, et al. Characterization of indeterminate (lipid-poor) adrenal masses: use of washout characteristics at contrast-enhanced CT. Radiology. 2000;217(3):798-802. https://doi.org/10.1148/radiology.217.3.r00dc29798 (retrieved 2026-10-05)"
  ],
  "related": [],
  "changelog": [
    {
      "date": "2026-10-05",
      "note": "Published after this site's editorial review against the cited sources (no clinician review); the page notices say so."
    }
  ]
}