Critical Limb Ischemia (CLI) represents the most advanced stage of peripheral arterial disease and requires immediate clinical attention. Early and accurate assessment of tissue perfusion is essential to prevent severe complications such as non-healing wounds or limb loss.
While the Ankle Brachial Index (ABI) is widely used in vascular diagnostics, it has important limitations — particularly in patients with diabetes or advanced vascular disease.
Why ABI Is Not Always Enough
ABI measures blood pressure at the ankle compared to the arm and is an established tool for detecting arterial obstruction. However, in certain patient populations, ABI values may be misleading.
In cases of medial arterial calcification — commonly seen in diabetes and elderly patients — arteries may become non-compressible. This can result in falsely elevated ABI values, masking underlying ischemia.
As a result, patients may present with normal or near-normal ABI despite significant impairment of distal circulation.
What Are Toe Pressure and TBI?
Toe pressure measurement assesses blood pressure at the level of the toes, providing insight into distal perfusion. Because digital arteries are less affected by calcification, toe pressure is often more reliable in patients where ABI is limited.
The Toe Brachial Index (TBI) is calculated similarly to ABI:
TBI = toe pressure / brachial pressure
This parameter allows clinicians to evaluate microcirculatory perfusion more accurately, particularly in high-risk patients.
A commonly used threshold for the toe-brachial index (TBI) is < 0.7, which is generally considered indicative of peripheral arterial disease and impaired distal perfusion.
Values below this threshold are associated with an increased likelihood of clinically relevant ischemia, particularly in patients with diabetes or suspected critical limb ischemia. Incorporating TBI cut-off values into clinical assessment supports more accurate diagnosis and risk stratification.
The Role in Critical Limb Ischemia
In CLI, assessing distal perfusion is crucial. Toe pressure and TBI help to:
- detect ischemia when ABI appears normal
- evaluate wound healing potential
- guide revascularization decisions
- monitor treatment outcomes
Low toe pressure values are strongly associated with poor tissue perfusion and increased risk of non-healing wounds or amputation.
Clinical Relevance
In everyday clinical practice, relying solely on ABI may lead to underdiagnosis of critical ischemia.
Integrating toe pressure and TBI into vascular assessment provides a more complete picture of circulatory status, particularly in patients with diabetes, chronic wounds or suspected CLI.
Integrated Vascular Assessment
A comprehensive evaluation of vascular health requires assessing both large vessel flow and distal perfusion.
Systems such as AngE™ ABI+ enable structured, non-invasive measurement of ABI, toe pressure and TBI within a single workflow — supporting efficient and reliable diagnostics.
Conclusion
Toe pressure and TBI are essential tools for detecting critical limb ischemia, especially when ABI alone is insufficient.
By incorporating these parameters into routine diagnostics, clinicians can improve early detection, support treatment decisions and ultimately enhance patient outcomes.
👉 Learn more: https://vascular-academy.com/
Sources:
https://imiit.org/diagnostic-testing/abi-tbi-exam/
https://www.ahajournals.org/doi/10.1161/cir.0000000000000470
