What does the ankle‑brachial index (ABI) assess?

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Last updated: September 17, 2026 • View editorial policy

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What the Ankle-Brachial Index Assesses

The ankle-brachial index (ABI) is a noninvasive diagnostic test that assesses lower-extremity arterial perfusion by comparing ankle to arm systolic blood pressures, serving as both a first-line diagnostic tool for peripheral arterial disease (PAD) and an independent predictor of cardiovascular morbidity and mortality. 1

Primary Clinical Applications

1. Diagnosis of Peripheral Arterial Disease

The ABI should be used as the first-line noninvasive test for diagnosing PAD when clinical suspicion exists based on symptoms and findings (Class I, Level A evidence). 1 The test measures:

  • Systolic blood pressure at the ankle (using posterior tibial and dorsalis pedis arteries)
  • Systolic blood pressure at the brachial artery
  • The ratio between these values (ankle pressure ÷ brachial pressure)

2. Diagnostic Thresholds

The ABI provides clear diagnostic cut-points 1:

  • ABI <0.90: Confirms diagnosis of lower-extremity PAD (Class I, Level A evidence)
  • ABI 0.91-1.00: "Borderline" cardiovascular risk requiring further evaluation (Class IIa, Level A evidence)
  • ABI 1.11-1.40: Normal range
  • ABI >1.40: Suggests arterial calcification; requires toe-brachial index or alternative testing (Class I, Level A evidence)

Cardiovascular Risk Stratification

Beyond PAD diagnosis, the ABI functions as a powerful independent marker of systemic atherosclerosis and cardiovascular risk 1:

  • Individuals with ABI <0.90 or >1.40 should be considered at increased risk of cardiovascular events and mortality, independent of PAD symptoms or other cardiovascular risk factors (Class I, Level A evidence) 1
  • The pooled hazard ratio for cardiovascular mortality with ABI ≤0.90 is 4.2 in men and 3.5 in women compared to normal ABI 1
  • The ABI provides incremental information beyond standard risk scores in predicting future cardiovascular events (Class IIA, Level A evidence) 1

Assessment of Lower-Extremity Perfusion

The ABI directly evaluates blood flow adequacy to the lower extremities 2:

  • Screens for arterial insufficiency before compression therapy application
  • Assesses wound healing potential in patients with lower-extremity wounds
  • Monitors disease progression over time
  • Evaluates treatment response after peripheral vascular interventions

Important Clinical Caveats

When ABI Results Are Unreliable

When ABI >1.40 despite clinical suspicion of PAD, arterial calcification (common in diabetes and chronic kidney disease) renders the test unreliable 1. In these cases:

  • Use toe-brachial index instead
  • Consider alternative imaging modalities
  • Do not rely on ABI alone for clinical decision-making

Exercise Testing Indications

When resting ABI is >0.90 but clinical suspicion for PAD persists, perform post-exercise ABI (Class I, Level A evidence) 1. Diagnostic criteria:

  • Post-exercise ankle pressure decrease >30 mm Hg, OR
  • Post-exercise ABI decrease >20% (Class IIa, Level A evidence)

Measurement Technique Essentials

For accurate assessment, the ABI requires proper technique 1:

  1. Measure systolic pressures in sequence: first arm → first posterior tibial → first dorsalis pedis → other posterior tibial → other dorsalis pedis → other arm
  2. Use the lower ABI of both legs to identify more individuals at cardiovascular risk
  3. Repeat first arm measurement if difference between arms exceeds 10 mm Hg (discard initial reading)
  4. Calculate using the higher brachial pressure as denominator for diagnostic specificity

Clinical Impact on Outcomes

The ABI directly relates to patient outcomes that matter 3, 4:

  • Mortality prediction: Lower ABI values correlate with higher cardiovascular and all-cause mortality in a nonlinear fashion
  • Functional status: ABI levels below 1.1 associate with poor physical function in cardiovascular disease patients 5
  • Kidney function: Declining ABI correlates with accelerated eGFR decline in chronic kidney disease 6
  • Limb outcomes: Intra-leg ABI asymmetry (≥0.15 difference between dorsalis pedis and posterior tibial) independently predicts major adverse limb events 7

The ABI remains critically underutilized despite its high specificity, reproducibility, and prognostic value 3, 8. When used correctly with proper technique and interpretation of threshold values, it provides invaluable information about both lower-limb perfusion and systemic cardiovascular risk that directly impacts mortality and quality of life.

References

2
Research

Ankle Brachial Index: Quick Reference Guide for Clinicians: WOCN Society Ankle Brachial Task Force.

Journal of wound, ostomy, and continence nursing : official publication of The Wound, Ostomy and Continence Nurses Society, 2025

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This information is intended for healthcare professionals. Any medical decision-making should rely on clinical judgment and independently verified information. The content provided herein does not replace professional discretion and should be considered supplementary to established clinical guidelines. Healthcare providers should verify all information against primary literature and current practice standards before application in patient care. Dr.Oracle assumes no liability for clinical decisions based on this content.