AHA/ACC StandardAnkle-Brachial Index (ABI) Perfusion Ratio
Hemodynamic Inputs
mmHg
Use the higher systolic pressure of either the DP or PT artery.
mmHg
Use the higher systolic pressure measured in either the left or right arm.
ABI Interpretation
Provide the ankle and brachial systolic pressures to compute the ankle-brachial index and obtain clinical classification.
Guidelines & Evidence
Verified
Last Review: 2026
When to Use
What is the Ankle-Brachial Index (ABI)?
The ankle-brachial index (ABI) is the ratio of systolic blood pressure measured at the ankle (posterior tibial or dorsalis pedis artery) to the systolic blood pressure measured in the arm (brachial artery). It is a simple, non-invasive, reproducible test for detecting lower extremity peripheral artery disease (PAD). A normal ABI ranges from 1.00 to 1.40. Values below 0.90 indicate PAD (sensitivity ~79%, specificity ~96% for angiographically significant stenosis >50%). Values >1.40 suggest non-compressible calcified vessels (common in diabetes, chronic kidney disease) and indicate falsely elevated ABI (requires toe-brachial index or other tests). The ABI also predicts cardiovascular morbidity and mortality (myocardial infarction, stroke, cardiovascular death), with lower ABI (even in the borderline range of 0.90-0.99) associated with increased risk.
Primary Clinical Indications
Screening for PAD in asymptomatic high-risk patients – USPSTF: Insufficient evidence for routine screening; AHA/ACC: Consider screening in patients aged ≥65 years, or ≥50 years with smoking history or diabetes (Class IIa, Level B)
Diagnosis of PAD in symptomatic patients – Patients with exertional leg pain (claudication: calf, thigh, or buttock pain that resolves with rest), non-healing foot ulcers, or rest pain (ischemic pain at night relieved by dangling foot)
Prognostic assessment for cardiovascular events – Low ABI (<0.90) is associated with 2-3x increased risk of myocardial infarction, stroke, and cardiovascular death, independent of Framingham risk factors
Assessment of PAD severity and functional limitation – Degree of ABI reduction correlates with severity of claudication and functional impairment (6-minute walk distance, walking speed)
Monitoring PAD progression or response to therapy – ABI changes >0.15 are considered clinically significant; improves after revascularization (angioplasty, stenting, bypass) or exercise therapy (modest improvement 0.05-0.10)
Evaluation for chronic limb-threatening ischemia (CLTI) – ABI <0.50 indicates severe PAD, often associated with rest pain, tissue loss, or gangrene
Pre-operative cardiovascular risk assessment (non-cardiac surgery) – Low ABI (<0.90) is a risk marker for perioperative cardiovascular events (though not included in RCRI, it adds prognostic value)
Screening first-degree relatives of PAD patients – Genetic component; siblings of PAD patients have 2-3x higher PAD prevalence
Contraindications / Limitations
Non-compressible vessels (falsely elevated ABI >1.40) – Common in diabetes, chronic kidney disease (CKD), elderly, and longstanding hypertension due to medial arterial calcification (Monckeberg's sclerosis). The ankle arteries cannot be compressed by the blood pressure cuff, giving falsely high readings. Toe-brachial index (TBI) or pulse volume recordings (PVR) are recommended in these cases.
Inability to perform test – Patients with bilateral above-knee amputations, severe leg contractures, or open wounds (where cuff placement may be contraindicated)
Acute limb ischemia – ABI may be unreliable in acute limb ischemia (due to pain, reactive hyperemia, or spasm; doppler waveform analysis is more useful)
Severe venous insufficiency or edema – May affect auscultation of doppler signals; still feasible but may be technically difficult
Atrial fibrillation – Beat-to-beat variability in blood pressure; require averaging of multiple beats (3-5) or using MAP (mean arterial pressure) method
Vasospastic conditions (Raynaud's) – Cold-induced vasospasm may falsely lower ABI; warm the patient before testing
Post-exercise ABI – After treadmill exercise (or toe raises), ABI may drop in patients with mild PAD who have normal resting ABI; requires standardized protocol (Gardner-Skinner protocol)
Not diagnostic for upper extremity PAD – ABI assesses lower extremity; upper extremity PAD (subclavian stenosis) requires different testing (arm-brachial index, bilateral brachial pressures)
Operator-dependent – Requires trained technician for accurate doppler waveform interpretation and pressure measurement
ABI Interpretation and Clinical Significance
| ABI Value | Interpretation | Clinical Significance | Recommended Action |
|---|---|---|---|
| <0.40 | Severe PAD | Critical limb-threatening ischemia (CLTI) – rest pain, non-healing ulcers, gangrene; high risk of limb loss | Urgent vascular surgery referral; angiography and revascularization (endovascular or surgical) typically required |
| 0.40-0.59 | Moderate-severe PAD | Severe claudication (walking <100 meters), rest pain possible; high cardiovascular risk | Vascular surgery referral; consider revascularization (endovascular vs surgical); optimize cardiovascular risk factors (smoking cessation, antiplatelet, statin) |
| 0.60-0.79 | Mild-moderate PAD | Claudication (walking 100-200 meters); increased CV risk; may have rest pain if diabetic or severe | Supervised exercise therapy (first-line for claudication); smoking cessation; antiplatelet therapy (aspirin or clopidogrel); statin; consider revascularization if lifestyle-limiting claudication |
| 0.80-0.89 | Borderline PAD (equivocal) | Possible mild PAD; may have atypical leg symptoms; increased CV risk (lower end of range) | Repeat ABI in 6-12 months; consider exercise ABI if symptoms suggestive; optimize CV risk factors; manage as high-risk for CV events |
| 0.90-0.99 | Low normal (some experts: borderline abnormal) | Generally considered normal; but ABI <0.99 is associated with increased CV risk (continuous relationship between ABI and CV events) | Reassess every 1-2 years if risk factors (diabetes, smoking); treat CV risk factors aggressively |
| 1.00-1.40 | Normal | No evidence of hemodynamically significant PAD (stenosis <50% likely) | Reassess if symptoms develop; consider ABI screening every 5 years in high-risk patients (diabetes, smoking, age >65) |
| 1.40-1.50 | Non-compressible (elevated) | Suggests medial arterial calcification; common in diabetes, CKD, elderly (prevalence 10-30% in diabetics over 60) | Calculate toe-brachial index (TBI) or use pulse volume recordings (PVR) for PAD detection; ABI not reliable (falsely elevated) |
| >1.50 | Non-compressible (severely elevated) | Highly likely to have calcified vessels; still at high CV risk despite normal/elevated ABI | TBI recommended (normal >0.60-0.70; <0.50 suggests PAD). Manage CV risk factors aggressively |
Last Comprehensive Review: 2026