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Toe Brachial IndexEdit

Toe Brachial Index

The Toe Brachial Index (TBI) is a noninvasive vascular test used to assess blood flow to the toes by comparing the systolic pressure at the toe to the systolic pressure in the brachial artery of the arm. It is most often employed to evaluate suspected peripheral arterial disease (PAD) in the lower extremities, particularly in patient groups where traditional measurements can be unreliable. In clinical practice, the TBI plays a crucial role alongside other noninvasive tests such as the Ankle-brachial index (Ankle-brachial index) and imaging studies, helping clinicians gauge limb perfusion and wound healing potential.

Because a patient’s toe arteries are smaller and less prone to certain artifacts than leg arteries, clinicians frequently turn to the TBI when arterial calcification in the lower legs (which can falsely elevate the ankle measurements) would otherwise obscure the diagnosis. The method integrates ideas from vascular physiology and noninvasive sensing to provide a practical gauge of distal limb perfusion, informing decisions about medical management, revascularization, and wound care. See also Peripheral artery disease and Doppler ultrasound for related diagnostic approaches, and Transcutaneous oxygen tension as another modality used to assess tissue perfusion.

Measurement and interpretation

Methodology

  • The patient is typically positioned to allow comfortable, stable Toe Brachial Index measurement, often lying supine after a short rest. The brachial systolic pressure is measured in the arms with a standard cuff and a Doppler probe to identify the peak systolic pressure.
  • Toe pressures are obtained from one or both toes using a small cuff placed around the toe (often the hallux or great toe) and a Doppler probe or other noninvasive sensing method such as photoplethysmography. Consistent probe placement and careful technique are essential for reliable results.
  • The toe systolic pressure is divided by the brachial systolic pressure to yield the Toe Brachial Index: TBI = toe systolic pressure / brachial systolic pressure.
  • If feasible, measurements from both feet or both toes may be averaged or used to confirm consistency. Values are interpreted in light of patient age, comorbidities, and clinical context.

In clinical practice, this approach is commonly contrasted with the Ankle-brachial index (Ankle-brachial index), which uses the ankle rather than the toe. The toe-based measurement tends to be more robust in patients with arteries that are not easily compressed due to calcification or in whom leg-based measurements are unreliable.

Normal values and thresholds

  • Normal TBI values are typically in the range of about 0.75 to 0.95.
  • Borderline or mildly reduced values are generally considered around 0.65 to 0.75.
  • Abnormally low values, often taken as <0.70, suggest reduced distal perfusion and the possible presence of PAD affecting the toe vessels.
  • Very low toe pressures (for example, well below 0.5) indicate severe impairment of distal perfusion and raise concern for advanced disease or critical limb-threatening ischemia, particularly when combined with clinical signs such as ischemic pain, nonhealing ulcers, or gangrene.
  • It is important to interpret TBI alongside other assessments—such as the patient’s symptoms, wound status, and findings from additional tests like duplex ultrasound (Doppler ultrasound) or TcPO2 in some cases.

Clinical indications

  • Evaluation of suspected peripheral arterial disease when leg or foot symptoms are present, such as intermittent claudication or rest pain.
  • Assessment of foot perfusion in patients with diabetes mellitus or other conditions that produce arterial calcification, where ABI may be unreliable.
  • Preoperative risk stratification and planning for procedures that rely on adequate distal perfusion.
  • Monitoring of perfusion in patients with foot ulcers or wounds to guide treatment decisions and prognosis.

Limitations and considerations

  • Toe measurements can be sensitive to environmental temperature, patient movement, and operator technique. Cold extremities or recent smoking can transiently reduce toe pressures.
  • In diabetic or elderly patients, small-vessel disease and microvascular dysfunction can affect toe pressures independently of large-vessel PAD.
  • Arterial calcification can, in some cases, affect the toe as well, though the toe arteries are less commonly noncompressible than those in the ankle region. Consequently, the TBI is generally more reliable than ABI in the presence of medial calcification.
  • In some patients, toe pressures may be unobtainable or unreliable due to edema, severe deformities, or extensive tissue loss. In such cases, clinicians turn to alternative approaches, such as duplex imaging or TcPO2 measurements, to assess limb perfusion.
  • The interpretation of thresholds can vary slightly between guidelines and institutions, so clinicians often consider the full clinical context rather than a single cut-off value.

Relationship to other tests

  • The combination of TBI with the ABI can improve diagnostic accuracy for PAD, particularly when concerns about vascular calcification limit the reliability of leg-based measurements.
  • Noninvasive imaging such as Doppler ultrasound and duplex ultrasonography can provide anatomic and hemodynamic detail that complements functional indices like the TBI.
  • For tissue oxygenation assessment and wound care planning, tests such as Transcutaneous oxygen tension (TcPO2) may be used alongside the TBI.

See also