When is toe pressure preferred over Ankle-Brachial Index (ABI)?

When Toe Pressure is Preferred Over ABI

Toe pressure/toe-brachial index (TBI) should be performed when the resting ABI is >1.40 (noncompressible arteries), which indicates arterial calcification that renders the ABI unreliable. 1

Primary Indication: Noncompressible Arteries

• When ABI >1.40, toe pressure with waveforms must be obtained because medial arterial calcification (Mönckeberg's sclerosis) makes ankle arteries stiff and resistant to compression, artificially elevating pressure readings and masking true peripheral arterial disease (PAD). 1

• This is a Class I (strongest) recommendation with B-level evidence from the 2024 ACC/AHA guidelines, making it the most definitive indication for choosing toe pressure over ABI. 1

High-Risk Populations Where Toe Pressure Should Be Strongly Considered

Diabetes Mellitus

• Patients with diabetes are particularly prone to medial arterial calcification affecting larger ankle arteries, while smaller digital arteries remain less calcified and more compressible. 1, 2

• The IWGDF guidelines recommend toe-brachial index ≥0.75 as a reliable test to exclude PAD in diabetic patients, whereas ABI may be falsely elevated or "falsely normalized" even when <1.40. 1

• A TBI <0.70 is considered abnormal and indicates PAD, providing more accurate assessment than ABI in this population. 1

Chronic Limb-Threatening Ischemia (CLTI)

• In patients with suspected CLTI, toe pressure/TBI with waveforms should be used in addition to ABI to assess arterial perfusion and establish the diagnosis (Class IIa recommendation). 1

• Toe pressure <30 mmHg is a hemodynamic criterion for CLTI and should prompt urgent vascular imaging and revascularization consideration. 1

• For wound healing prediction in CLTI, toe pressure ≥30 mmHg increases the probability of healing by at least 25%, making it more clinically useful than ABI for prognostication. 1

Chronic Kidney Disease/End-Stage Renal Disease

• These patients have high rates of arterial calcification similar to diabetes, making ABI unreliable and toe pressure the preferred measurement. 1, 3

Clinical Scenarios Requiring Toe Pressure Assessment

When ABI is Normal but Clinical Suspicion Remains High

• If a patient has symptoms suggestive of PAD (exertional leg pain, non-healing wounds, rest pain) but ABI is 0.91-1.40, consider that arterial calcification may be "normalizing" a truly abnormal value. 1, 4

• In diabetic patients with foot ulcers, even a seemingly normal ABI may be misleading; toe pressure provides more accurate assessment of tissue perfusion. 1

Wound Healing Assessment

• Toe pressure ≥30 mmHg predicts wound healing potential, while values <30 mmHg suggest need for revascularization before wounds will heal. 1

• Skin perfusion pressure ≥40 mmHg and toe pressure ≥30 mmHg are the most useful bedside tests for predicting ulcer healing in diabetic foot ulcers. 1

Measurement Technique Advantages

• Toe pressure measurement using photoplethysmography (PPG) has excellent interrater reliability (ICC 0.93) and intrarater reliability (ICC 0.78-0.79) in diabetic patients, actually superior to brachial pressure measurements. 2

• Digital arteries are less affected by medial calcification compared to tibial arteries, providing more accurate reflection of true arterial perfusion. 5, 4

Critical Pitfalls to Avoid

• Do not rely solely on ABI in diabetic patients, even when <1.40, as calcification can occur at lower ABI values and still produce falsely reassuring results. 6, 4

• Do not assume normal ABI excludes PAD in high-risk populations (diabetes, chronic kidney disease, elderly patients) without considering toe pressure measurement. 1, 4

• Failing to measure toe pressure when ABI >1.40 is a critical error that will miss significant PAD and delay necessary interventions. 1

Practical Algorithm for Decision-Making

1. Measure resting ABI first in all patients with suspected PAD. 1

2. If ABI >1.40: Automatically proceed to toe pressure/TBI measurement (mandatory). 1

3. If ABI 0.91-1.40 AND patient has diabetes, chronic kidney disease, or non-healing wounds: Strongly consider toe pressure for more accurate assessment. 1

4. If ABI ≤0.90: ABI is reliable for diagnosis, but add toe pressure if assessing CLTI or wound healing potential. 1

5. For any patient with suspected CLTI: Measure both ABI and toe pressure regardless of initial ABI value. 1

Interpretation Thresholds

• Normal TBI: ≥0.70 (some sources use ≥0.75 for diabetic patients). 1
• Abnormal TBI: <0.70, indicating PAD. 1
• Critical ischemia threshold: Toe pressure <30 mmHg, requiring urgent vascular evaluation. 1
• Wound healing threshold: Toe pressure ≥30 mmHg suggests reasonable healing potential. 1