6.2 Ankle-Brachial Index (ABI) & Toe-Brachial Index (TBI)
Key Takeaways
Report ABI as abnormal ≤0.90, borderline 0.91–0.99, normal 1.00–1.40, or noncompressible >1.40.
Calculate each ABI with the higher ipsilateral ankle pressure divided by the higher valid brachial pressure.
For suspected PAD with noncompressible ABI, obtain toe pressure/TBI with waveforms; TBI ≤0.70 is abnormal.
Toe pressure <30 mmHg indicates severe ischemia and poorer healing probability, not a guarantee that healing is impossible.
Interpret pressure measurements with symptoms, wounds, waveforms, and technical limitations.
What ABI measures
The ankle-brachial index (ABI) compares ankle systolic pressure with brachial systolic pressure. It is a physiologic assessment of lower-extremity arterial perfusion, not a direct image of a particular lesion. The 2024 multisociety PAD guideline uses four reporting categories. Preserve the distinction between normal and borderline rather than calling every value above 0.90 normal.
| Resting ABI | Category |
|---|---|
| ≤0.90 | Abnormal |
| 0.91–0.99 | Borderline |
| 1.00–1.40 | Normal |
| >1.40 | Noncompressible |
Some laboratories further describe mild, moderate, or severe pressure impairment within the abnormal category. Such subdivisions do not independently establish the clinical syndrome. Chronic limb-threatening ischemia (CLTI) requires an appropriate clinical presentation, such as ischemic rest pain or tissue loss, with objective evidence of ischemia. An ABI alone cannot diagnose every case or exclude CLTI.
Standard acquisition
Review the indication, symptoms, prior interventions, wounds, dialysis access, and factors affecting cuff placement. Allow supine rest and keep the arms and ankles near heart level. Use appropriately sized cuffs and a continuous-wave Doppler device. Avoid placing cuffs over vulnerable wounds or a dialysis access, and follow the clinical plan when a standard measurement is unsafe or unobtainable.
Measure systolic pressures in both brachial arteries and in the dorsalis pedis and posterior tibial arteries of each leg. Inflate sufficiently to extinguish the signal within the device's safe protocol, then deflate slowly while detecting its return. Recheck unexpected values. Excessive probe pressure can eliminate a weak signal; a poorly directed probe can create an apparent absence of flow.
For each leg:
Use the higher valid ankle pressure on that leg and the higher valid brachial pressure from the two arms. Record individual pressures and waveforms as well as the ratio. A low pressure in one arm can reflect inflow disease; using it as the denominator artificially elevates the ABI. If both brachial measurements are unreliable or unavailable, document the limitation rather than inventing a denominator.
Worked calculation
Right brachial pressure is 132 mmHg and left brachial pressure is 148 mmHg. Left dorsalis pedis pressure is 84 mmHg and left posterior tibial pressure is 74 mmHg. The higher ankle pressure is 84 and the higher brachial pressure is 148. Left ABI = 84/148 = 0.5676, reported as 0.57. This is abnormal. Using 84/132 = 0.64 would overestimate the ratio.
Noncompressible vessels and discordance
Diabetes and chronic kidney disease increase the likelihood of noncompressible tibial arteries. A falsely high ankle pressure may coexist with major occlusive disease. If Doppler flow persists despite the protocol's safe maximum cuff pressure, report an unobtainable/noncompressible pressure; do not keep escalating pressure simply to force a number. When PAD is suspected with ABI above 1.40, obtain toe pressure/TBI with waveforms as recommended.
A numerical ABI within the normal range also does not exclude every perfusion problem. Symptoms, wounds, pedal waveforms, and toe pressure may disagree with ankle pressure. In a patient with exertional nonjoint leg symptoms and a normal or borderline resting ABI, exercise ABI can uncover disease. In suspected CLTI, additional perfusion measures help evaluate limb threat and healing potential.
Toe pressure and toe-brachial index
The toe-brachial index (TBI) is toe systolic pressure divided by the higher brachial pressure. Digital arteries are less often noncompressible than tibial arteries, but they are not immune to disease or calcification. Use a small toe cuff and a suitable sensor, commonly photoplethysmography. Maintain a warm environment, avoid motion and excessive sensor pressure, and confirm that the waveform represents pulsatile flow.
A TBI ≤0.70 is abnormal in the 2024 PAD guideline. Absolute toe pressure below 30 mmHg indicates severe ischemia and is associated with poorer healing and higher amputation risk. It does not prove that healing is impossible or that one specific procedure is mandatory. Infection, wound depth, edema, microcirculation, nutrition, and overall health also affect outcomes.
For a toe pressure of 22 mmHg and brachial pressure of 144 mmHg, TBI = 22/144 = 0.15. In a patient with a nonhealing ulcer, this supports severe ischemia and prompt vascular evaluation. A falsely high ABI of 1.48 should not be used to reassure the patient. Record the toe waveform and measurement quality rather than relying on the ratio alone.
Technical traps and reporting
| Problem | Likely effect or response |
|---|---|
| Cuff too narrow | Can falsely elevate pressure; select an appropriate bladder size |
| Cold toes | Vasoconstriction may reduce signal and pressure; warm and reassess when appropriate |
| Motion or sensor artifact | Can obscure return of pulsatile signal; stabilize and repeat |
| Noncompressible ankle arteries | ABI may overstate perfusion; obtain toe measurements/waveforms |
| Amputation, wound, or absent usable toe signal | State the limitation and consider another perfusion method through the clinician |
| Severe pain or acute deterioration | Stop or modify testing and escalate appropriately |
Pulse volume recordings (PVRs), pedal Doppler waveforms, transcutaneous oxygen pressure, and skin perfusion pressure provide complementary evidence. No test substitutes for the history and physical examination. Report the side, individual pressures, calculated ratios, waveform findings, technical limitations, and comparison. New severe ischemic symptoms or threatened tissue require timely clinical communication rather than a routine report alone.
2024 multisociety lower-extremity PAD guideline — checked October 18, 2026.
A vascular technologist obtains the following baseline systolic blood pressures on a 62-year-old female presenting with exertional left calf cramping:
- Right Brachial: 132 mmHg
- Left Brachial: 148 mmHg
- Right DPA: 122 mmHg, Right PTA: 128 mmHg
- Left DPA: 84 mmHg, Left PTA: 74 mmHg
What is the correctly calculated Ankle-Brachial Index for the left lower extremity?
0.50
0.54
0.64
0.57
An 82-year-old male with end-stage renal disease on chronic hemodialysis presents with a non-healing necrotic ulcer over his left great toe. During non-invasive arterial testing, the vascular technologist inflates the ankle cuffs to 250 mmHg, but strong continuous-wave Doppler signals persist uninterrupted in both pedal arteries. What is the most appropriate next step in clinical evaluation?
Document the ankle vessels as incompressible (ABI > 1.40) and immediately perform a Toe-Brachial Index (TBI) using photoplethysmography
Report an ABI of 1.00 because persistent audible arterial flow excludes significant occlusive disease
Inflate the ankle cuff to 300 mmHg using an external high-pressure inflator to force arterial collapse
Conclude that the patient has normal lower extremity arterial perfusion and recommend local wound care
A 71-year-old diabetic female has a non-healing neuroischemic ulcer on her right first interdigital space. Bilateral resting ABIs are 1.48 on the right and 1.52 on the left. A Toe-Brachial Index examination is performed, demonstrating a right great toe systolic pressure of 22 mmHg against a highest brachial pressure of 144 mmHg. How should these findings be interpreted regarding wound healing potential?
ABI >1.40 excludes disease
TBI 0.15 and toe pressure 22 mmHg support severe ischemia and poor healing potential, requiring prompt clinical evaluation
Toe measurements are always invalid in diabetes
Only compression wraps are needed
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