{
  "id": "abi",
  "version": "5c9ee647bc4b",
  "status": "published",
  "name": "ABI Calculator",
  "question": "What is the ABI?",
  "summary": "Works out the ankle-brachial index (ABI) for each leg from the arm and ankle systolic pressures, as the 2016 AHA/ACC guideline on peripheral artery disease defines it, and grades each result.",
  "category": "health",
  "subcategory": "clinical",
  "url": "https://www.acalculator.org/health/abi-calculator",
  "markdown": "https://www.acalculator.org/health/abi-calculator.md",
  "kind": "function",
  "method": "ABI (each leg) = higher of the dorsalis pedis and posterior tibial systolic pressures ÷ higher of the right and left arm systolic pressures. Rounded to 2 decimals, then graded: 0.90 or less abnormal, 0.91 to 0.99 borderline, 1.00 to 1.40 normal, over 1.40 noncompressible.",
  "assumptions": [
    "Systolic pressures measured with a cuff and a Doppler probe while lying down.",
    "Each ABI is rounded once to 2 decimals (halves up) from the exact ratio of the typed pressures, then graded."
  ],
  "inputs": {
    "$schema": "https://json-schema.org/draft/2020-12/schema",
    "type": "object",
    "properties": {
      "rarm": {
        "title": "Right arm (brachial)",
        "description": "Right brachial artery. Systolic pressure in mmHg, 20 to 300.",
        "type": "number",
        "minimum": 20,
        "maximum": 300
      },
      "larm": {
        "title": "Left arm (brachial)",
        "description": "Left brachial artery. Systolic pressure in mmHg, 20 to 300.",
        "type": "number",
        "minimum": 20,
        "maximum": 300
      },
      "rpt": {
        "title": "Right ankle, posterior tibial",
        "description": "Right posterior tibial artery. Systolic pressure in mmHg, 20 to 300.",
        "type": "number",
        "minimum": 20,
        "maximum": 300
      },
      "rdp": {
        "title": "Right ankle, dorsalis pedis",
        "description": "Right dorsalis pedis artery. Systolic pressure in mmHg, 20 to 300.",
        "type": "number",
        "minimum": 20,
        "maximum": 300
      },
      "lpt": {
        "title": "Left ankle, posterior tibial",
        "description": "Left posterior tibial artery. Systolic pressure in mmHg, 20 to 300.",
        "type": "number",
        "minimum": 20,
        "maximum": 300
      },
      "ldp": {
        "title": "Left ankle, dorsalis pedis",
        "description": "Left dorsalis pedis artery. Systolic pressure in mmHg, 20 to 300.",
        "type": "number",
        "minimum": 20,
        "maximum": 300
      }
    }
  },
  "outputs": {
    "lowest": {
      "label": "ABI (lower leg)",
      "description": "The lower of the two legs’ ABI, to 2 decimals.",
      "format": "number"
    },
    "right": {
      "label": "Right ABI",
      "description": "Higher right ankle pressure ÷ higher arm pressure, to 2 decimals.",
      "format": "number"
    },
    "rightGrade": {
      "label": "Right leg",
      "description": "The guideline grade of the right ABI.",
      "format": "text"
    },
    "left": {
      "label": "Left ABI",
      "description": "Higher left ankle pressure ÷ higher arm pressure, to 2 decimals.",
      "format": "number"
    },
    "leftGrade": {
      "label": "Left leg",
      "description": "The guideline grade of the left ABI.",
      "format": "text"
    }
  },
  "defaultAnswer": {
    "inputs": {
      "rarm": 130,
      "larm": 128,
      "rpt": 120,
      "rdp": 118,
      "lpt": 100,
      "ldp": 104
    },
    "outputs": {
      "lowest": 0.8,
      "right": 0.92,
      "rightGrade": "Borderline",
      "left": 0.8,
      "leftGrade": "Abnormal"
    },
    "text": "The ABI is 0.92 on the right (Borderline) and 0.8 on the left (Abnormal)."
  },
  "examples": [
    {
      "given": {
        "rarm": 130,
        "larm": 128,
        "rpt": 120,
        "rdp": 118,
        "lpt": 100,
        "ldp": 104
      },
      "expect": {
        "lowest": 0.8,
        "right": 0.92,
        "rightGrade": "Borderline",
        "left": 0.8,
        "leftGrade": "Abnormal"
      },
      "source": "2016 AHA/ACC guideline rule: right 120 ÷ 130 = 0.923 → 0.92 borderline; left 104 ÷ 130 = 0.80 abnormal (hand calculation in content.mdx)"
    },
    {
      "given": {
        "rarm": 120,
        "larm": 124,
        "rpt": 130,
        "rdp": 126,
        "lpt": 128,
        "ldp": 132
      },
      "expect": {
        "lowest": 1.05,
        "right": 1.05,
        "rightGrade": "Normal",
        "left": 1.06,
        "leftGrade": "Normal"
      },
      "source": "130 ÷ 124 = 1.048 → 1.05; 132 ÷ 124 = 1.065 → 1.06 (hand calculation in content.mdx)"
    },
    {
      "given": {
        "rarm": 140,
        "larm": 140,
        "rpt": 126,
        "rdp": 120,
        "lpt": 200,
        "ldp": 210
      },
      "expect": {
        "right": 0.9,
        "rightGrade": "Abnormal",
        "left": 1.5,
        "leftGrade": "Noncompressible"
      },
      "source": "126 ÷ 140 = 0.90 (0.90 or less is abnormal); 210 ÷ 140 = 1.50, over 1.40 (hand calculation)"
    },
    {
      "given": {
        "rarm": 100,
        "larm": 98,
        "rpt": 99,
        "rdp": 90,
        "lpt": 140,
        "ldp": 135
      },
      "expect": {
        "right": 0.99,
        "rightGrade": "Borderline",
        "left": 1.4,
        "leftGrade": "Normal"
      },
      "source": "Band edges: 99 ÷ 100 = 0.99 borderline; 140 ÷ 100 = 1.40 normal (hand calculation in content.mdx)"
    },
    {
      "given": {
        "rarm": 200,
        "larm": 180,
        "rpt": 181,
        "rdp": 170,
        "lpt": 199,
        "ldp": 150
      },
      "expect": {
        "right": 0.91,
        "rightGrade": "Borderline",
        "left": 1,
        "leftGrade": "Normal"
      },
      "source": "Rounded once to 2 decimals, halves up, then graded (hand calculation in content.mdx)"
    }
  ],
  "sources": [
    "Gerhard-Herman MD, Gornik HL, Barrett C, et al. 2016 AHA/ACC guideline on the management of patients with lower extremity peripheral artery disease. Circulation. 2017;135(12):e726-e779. https://doi.org/10.1161/CIR.0000000000000471 (open at https://pmc.ncbi.nlm.nih.gov/articles/PMC5477786/, retrieved 2026-10-05)",
    "Aboyans V, Criqui MH, Abraham P, et al. Measurement and interpretation of the ankle-brachial index: a scientific statement from the American Heart Association. Circulation. 2012;126(24):2890-2909. https://doi.org/10.1161/CIR.0b013e318276fbcb (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."
    }
  ]
}