What is the recommended evaluation and management for a patient with an abnormal toe‑brachial index (TBI < 0.7)?

Management of Abnormal Toe-Brachial Index (TBI < 0.7)

An abnormal TBI ≤0.70 confirms the diagnosis of peripheral artery disease (PAD) and mandates initiation of guideline-directed medical therapy (GDMT) for cardiovascular risk reduction, along with evaluation for potential revascularization if symptoms or tissue loss are present. 1, 2

Diagnostic Confirmation and Interpretation

• A TBI ≤0.70 is the established threshold for diagnosing PAD, particularly valuable when ankle-brachial index (ABI) is unreliable due to noncompressible arteries (ABI >1.4), which commonly occurs in diabetes and chronic kidney disease. 1, 2

• More refined TBI thresholds based on recent data suggest: normal TBI >0.8, borderline 0.61-0.8, abnormal ≤0.6, and severe PAD ≤0.2, with a TBI <0.6 having 95% positive predictive value for PAD. 3

• TBI can be obtained in 92.7% of patients overall and in 82% of limbs where ABI is unobtainable, making it highly feasible for PAD diagnosis. 3

Immediate Clinical Actions

Cardiovascular Risk Stratification and Medical Therapy

• Initiate comprehensive GDMT immediately, as patients with abnormal TBI have significantly increased cardiovascular morbidity and mortality compared to those with normal values. 1

• Implement aggressive atherosclerotic risk factor modification including:

  • Antiplatelet therapy
  • High-intensity statin therapy
  • Blood pressure control
  • Diabetes management if present
  • Smoking cessation 1

Prognostic Implications

• Low TBI is associated with significantly decreased patient survival (42±20 versus 51±16 months in patients with normal TBI, p=0.011), independent of ABI values. 4

• Isolated low TBI (TBI <0.75 with ABI ≥0.90) carries similar mortality risk as combined foot-leg ischemia (both TBI and ABI abnormal), with progressive decline in survival across ischemia severity groups. 4

Symptom Assessment and Revascularization Evaluation

For Asymptomatic Patients

• Apply GDMT and preventive foot care as primary management strategy. 1

• Monitor for development of symptoms including claudication, rest pain, or tissue loss. 1

For Symptomatic Patients or Tissue Loss

• Refer for vascular imaging (duplex ultrasound, CT angiography, or conventional angiography) to define anatomic disease and plan potential revascularization. 1, 2

• Patients with isolated low TBI require revascularization at rates similar to those with low ABI, with angioplasty rates of 19.4% versus 3.2% in non-ischemic patients (p=0.033). 4

• For chronic limb-threatening ischemia (CLTI), additional hemodynamic criteria include:

  • Ankle pressure <50 mmHg
  • Toe pressure <30 mmHg
  • Transcutaneous oxygen pressure (TcPO₂) <30 mmHg 2

Special Populations

Diabetic Patients

• TBI demonstrates superior validity in diabetics compared to ABI, with sensitivity 0.88, specificity 0.88, and negative predictive value 0.97 for detecting significant stenosis. 5

• Diabetic patients with foot ulceration and isolated low TBI achieve similar healing rates to non-ischemic patients (68% versus 60% over 12 months) when appropriately revascularized. 4

Patients with Renal Disease

• TBI is particularly valuable in dialysis populations where vessel calcification renders ABI unreliable, though measurement protocols require standardization. 6

Critical Pitfalls to Avoid

• Do not rely solely on ABI in patients with diabetes or chronic kidney disease, as noncompressible tibial arteries frequently produce falsely elevated ABI >1.4 despite significant PAD. 1, 2

• Do not dismiss borderline TBI values (0.61-0.8) as these patients may still have clinically significant disease requiring close monitoring. 3

• Do not delay GDMT initiation while awaiting further vascular imaging, as cardiovascular risk reduction should begin immediately upon PAD diagnosis. 1

• Ensure proper measurement technique with 5-10 minutes supine rest, photoplethysmography probe on distal pulp of first or second toe, and comparison to higher brachial pressure. 2

Wound Healing Assessment

• For patients with wounds, TBI >0.6 generally indicates adequate perfusion for healing potential, while TBI <0.6 typically requires revascularization consideration. 3, 7

• Resting TcPO₂ >30 mmHg is a favorable indicator of wound healing, while <10 mmHg is associated with poor prognosis for healing and amputation risk. 2