What toe‑brachial index values define abnormal peripheral arterial disease, and does a right‑leg TBI of 0.77 indicate abnormal?

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Last updated: May 24, 2026 • View editorial policy

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TBI Threshold for Abnormal PAD: Your Patient's 0.77 Value is Normal

A TBI of 0.77 in your patient's right leg is normal and does not indicate peripheral arterial disease. The established threshold for abnormal TBI is ≤0.70, not 0.80 1, 2, 1.

Understanding the TBI Thresholds

The confusion about two thresholds stems from different contexts:

The Definitive Abnormal Threshold: ≤0.70

  • TBI ≤0.70 is diagnostic of PAD 1, 2, 1
  • This threshold is consistently recommended across major guidelines (2016-2024 AHA/ACC guidelines)
  • Digital arteries are rarely noncompressible, making this cutoff reliable even in patients with diabetes or chronic kidney disease where ankle pressures may be falsely elevated 1, 2

The 0.80 Reference Point

The 0.80 value appears in research literature as:

  • An upper limit of normal in some studies (TBI >0.80 = normal) 3
  • A borderline zone between 0.70-0.80 in proposed classification schemes 3
  • However, this is NOT the guideline-recommended diagnostic threshold

Your Patient's Result: 0.77

With a TBI of 0.77, your patient falls into what some researchers call a "borderline" zone, but by guideline standards, this is normal because it exceeds the 0.70 cutoff 1, 2.

Clinical Interpretation:

  • No PAD diagnosed by TBI criteria (value >0.70)
  • If clinical suspicion remains high despite this normal TBI, consider:
    • Ankle-brachial index (ABI) measurement if not already done
    • Exercise treadmill ABI testing if symptoms are exertional 1, 2
    • Alternative causes of symptoms if present

When TBI is Most Useful

TBI should be measured when 1, 2:

  • ABI is >1.40 (noncompressible arteries)
  • Patients have longstanding diabetes mellitus
  • Patients have advanced chronic kidney disease
  • There's clinical suspicion of PAD despite normal/borderline ABI

Important Caveats

  • Measurement conditions matter: TBI should be obtained in a warm room to prevent arterial vasoconstriction 1
  • Context is critical: A TBI of 0.77 with nonhealing wounds would warrant further evaluation even though technically "normal," as wound healing probability decreases with toe pressure <30 mmHg (which corresponds to lower TBI values) 1
  • The 0.70 threshold has high specificity (93-97%) but moderate sensitivity (45-80%) for PAD 4, 5, meaning values just above 0.70 don't completely exclude disease in all cases

Bottom line: Your patient's TBI of 0.77 does not meet criteria for abnormal PAD by current guideline standards, which define abnormal as ≤0.70.

References

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This information is intended for healthcare professionals. Any medical decision-making should rely on clinical judgment and independently verified information. The content provided herein does not replace professional discretion and should be considered supplementary to established clinical guidelines. Healthcare providers should verify all information against primary literature and current practice standards before application in patient care. Dr.Oracle assumes no liability for clinical decisions based on this content.