AHA/ACC StandardToe-Brachial Index (TBI) Diagnostic Ratio
Toe Perfusion Inputs
mmHg
Measured in the great toe (hallux) via photoplethysmography (PPG).
mmHg
Use the higher systolic pressure measured in either arm.
TBI Interpretation
Provide the toe and brachial systolic pressures to compute the toe-brachial index and obtain clinical classification.
Guidelines & Evidence
Verified
Last Review: 2026
When to Use
What is the Toe-Brachial Index (TBI)?
The toe-brachial index (TBI) is the ratio of systolic blood pressure measured at the great toe (using a small pneumatic cuff and photoplethysmography (PPG) sensor) to the systolic blood pressure in the arm (brachial artery). It is used to diagnose peripheral artery disease (PAD) when the ankle-brachial index (ABI) is unreliable due to non-compressible calcified ankle arteries. Medial arterial calcification (Monckeberg's sclerosis) is common in patients with diabetes mellitus (prevalence 10-30% in diabetics over 60), chronic kidney disease (CKD, especially on dialysis, 50-70%), and elderly patients (>75 years). These calcified vessels cannot be compressed by the blood pressure cuff, resulting in falsely elevated (or normal) ABI (>1.40) even in the presence of significant PAD. The toe arteries are less prone to calcification, making TBI a more accurate test in these populations. A normal TBI is typically >0.60-0.70; values <0.50-0.60 indicate PAD (depending on the study and threshold used).
Primary Clinical Indications
Non-compressible ankle arteries (ABI >1.40) – Most common indication. Patients with diabetes, CKD, or advanced age often have calcified vessels, making ABI unreliable. TBI is recommended in these cases (AHA/ACC Class I, Level B).
Suspected PAD in diabetic patients with normal or high ABI – Up to 30% of diabetic patients over age 60 have non-compressible vessels; TBI can unmask PAD in this population.
Evaluation of chronic limb-threatening ischemia (CLTI) – TBI is more sensitive than ABI in detecting severe PAD when ABI may be falsely elevated due to calcification. TBI <0.50 is consistent with CLTI (rest pain, ulcer, gangrene).
Assessment of wound healing potential – Toe pressure >40-50 mmHg (TBI >0.50-0.60) is generally required for healing of foot ulcers; toe pressure <30 mmHg (TBI <0.30-0.40) indicates critical ischemia and poor healing without revascularization.
Screening for PAD in high-risk patients with diabetes (especially if ABI cannot be performed or is equivocal) – Some guidelines recommend TBI as first-line in diabetic patients (though ABI remains first-line in most), but TBI is complementary.
Monitoring after revascularization (endovascular or surgical) in diabetic patients – If ABI is unreliable due to calcification, TBI can be used to assess hemodynamic improvement (target toe pressure >50-60 mmHg).
Research and clinical trials – Some PAD trials use TBI as an endpoint, especially in diabetic cohorts where ABI may be unreliable.
Contraindications / Limitations
Cannot be performed in patients with prior toe amputation – Need at least one great toe (or other toe if great toe missing) for PPG sensor placement. If no toes, TBI cannot be calculated (use pulse volume recordings (PVR) or duplex ultrasound instead).
Requires specialized equipment – Photoplethysmography (PPG) sensor and small pediatric-sized cuffs (typically 2-4 cm wide). Not all vascular labs or clinics have this equipment; ABI is more widely available.
Affected by toe movement – Patient must remain still during measurement; toe movement (voluntary or involuntary) creates PPG artifact and inaccurate pressure readings.
Technically more challenging than ABI – Requires more patient cooperation and operator skill; may be difficult in patients with Parkinson's disease, tremors, or agitation.
Not reliable in patients with severe vasoconstriction (cold extremities) – Vasoconstriction reduces PPG signal amplitude; warm the patient or room before testing.
No universally accepted threshold – Thresholds vary across studies: some use <0.60, others <0.70 for abnormal. For toe pressure, commonly used thresholds are <50 mmHg (some use <55 mmHg) for CLTI and <30 mmHg for critical ischemia.
Lower sensitivity for mild PAD (50-69% stenosis) – TBI is less sensitive than ABI for mild to moderate PAD; its primary use is in severe PAD and non-compressible vessels.
Not recommended as a first-line screening test for the general population – ABI is sufficient in most patients; TBI reserved for those with non-compressible vessels or high clinical suspicion with normal/equivocal ABI.
TBI vs ABI vs Toe Pressure
| Test | Formula | Normal Range | Abnormal (PAD) | Advantages | Disadvantages |
|---|---|---|---|---|---|
| ABI (Ankle-Brachial Index) | (Highest ankle pressure) / (Highest brachial pressure) | 1.00-1.40 | <0.90 (PAD); >1.40 (non-compressible) | Simple, widely available, well-validated, first-line test | Not reliable in calcified vessels (diabetes, CKD, elderly); requires doppler probe |
| TBI (Toe-Brachial Index) | (Great toe pressure) / (Highest brachial pressure) | >0.60-0.70 (varies by source) | <0.50-0.60 (PAD) | Unaffected by calcified vessels; sensitive for CLTI (rest pain, ulcers) | Requires PPG, not widely available, technically more challenging, less validated than ABI |
| Absolute Toe Pressure (mmHg) | Direct measurement (mmHg) | >60-70 mmHg (normal) | <50 mmHg (PAD/CLTI); <30 mmHg (critical ischemia) | Absolute threshold (not dependent on arm pressure), intuitive for wound healing (need >40-50 mmHg for healing) | Requires PPG, varies with arm pressure (but threshold absolute, not ratio) |
| Pulse Volume Recording (PVR) | Waveform analysis (not a ratio) | Triphasic waveform (normal) | Monophasic or flat waveform (PAD) | Unaffected by calcification (measures pulse volume, not pressure) | Qualitative (not quantitative), requires interpretation, less standardized |
Last Comprehensive Review: 2026