Is a discrepancy in Toe-Brachial Index (TBI) values between the left (0.99) and right (0.77) limbs, with a normal Ankle-Brachial Index (ABI), a problem in a patient with grade 1 diastolic dysfunction, iron deficiency anemia, and low stroke volume index?

Is a TBI Discrepancy Between Limbs Clinically Significant?

Yes, your right TBI of 0.77 is abnormal and indicates peripheral arterial disease (PAD) in that limb, despite your normal ABI values, and this discrepancy warrants further vascular evaluation with duplex ultrasound or other imaging to assess the location and severity of arterial stenosis. 1

Understanding Your Results

Normal ABI Can Miss PAD

• Your normal ABI values do not exclude PAD, particularly when TBI values are abnormal 1
• In patients with chronic limb-threatening ischemia, approximately 40% have normal ABIs, demonstrating that ABI alone is inadequate for comprehensive vascular assessment 1
• Research shows that 43% of symptomatic PAD patients with ≥50% arterial stenosis on imaging have normal or inconclusive resting ABIs 2
• The concordance between ABI and TBI is poor, with only 58% of patients meeting criteria for abnormal toe pressures also presenting with abnormal ABIs 1

TBI Interpretation Standards

• Normal TBI: ≥0.70 (some sources suggest ≥0.75 for higher specificity) 1
• Abnormal TBI: <0.70 indicates PAD 1
• Your left TBI of 0.99 is normal, indicating adequate arterial perfusion to that limb 1
• Your right TBI of 0.77 falls into a borderline/mildly abnormal range, suggesting early arterial disease 3

Clinical Significance of the Discrepancy

The asymmetry between your limbs is clinically meaningful:

• A TBI of 0.77 on the right suggests arterial stenosis distal to the ankle, even though ankle pressures appear normal 4, 3
• Research demonstrates that limbs with PAD (ABI ≤0.9) have TBI <0.8 in 99.5% of cases, and your right limb falls just above this threshold 3
• The negative predictive value of TBI ≥0.8 for excluding PAD is 0.99, meaning your right TBI of 0.77 has meaningful diagnostic implications 3

Why This Matters in Your Clinical Context

Your Risk Factors Increase Concern

Given your comorbidities (grade 1 diastolic dysfunction, iron deficiency anemia, low stroke volume index):

• Reduced cardiac output from diastolic dysfunction may compromise peripheral perfusion 1
• Anemia reduces oxygen-carrying capacity, potentially exacerbating tissue ischemia in areas with borderline perfusion 1
• These factors make even borderline arterial insufficiency more clinically significant 1

ABI May Be "Falsely Normalized"

• Early arterial calcification can stiffen vessels enough to normalize an otherwise low ABI, while digital arteries (measured by TBI) remain compressible and reveal the true perfusion deficit 4, 2
• In patients with diabetes or chronic kidney disease, this phenomenon is particularly common, though you haven't mentioned these conditions 1, 4

Recommended Next Steps

Immediate Actions

1. Obtain duplex ultrasound of the right lower extremity to identify the location and severity of arterial stenosis 1

   • This will determine if stenosis is in the tibial, peroneal, or pedal arteries 1
   • Duplex has 85-90% sensitivity and >95% specificity for detecting stenosis >50% 1

2. Consider segmental pressures with pulse volume recordings (PVR) to localize the level of disease 1

   • This helps distinguish between femoropopliteal versus infrapopliteal disease 1
   • PVR is particularly useful as it's not affected by arterial calcification 1

Cardiovascular Risk Assessment

• Even borderline PAD detected by TBI is associated with increased cardiovascular morbidity and mortality 1
• Initiate or optimize guideline-directed medical therapy (GDMT) including antiplatelet therapy, statin therapy, and blood pressure control 1
• Address modifiable risk factors, particularly smoking cessation if applicable 1

Monitoring Strategy

• Repeat TBI measurements on both limbs to establish a baseline trend 5
• Research suggests taking at least two readings per foot, and if discrepant, additional readings are recommended 5
• Serial measurements over time provide more accurate assessment than single measurements 6, 5
• Monitor for development of symptoms such as claudication, rest pain, or non-healing wounds 1

Common Pitfalls to Avoid

• Do not dismiss the abnormal TBI simply because the ABI is normal – this is a well-documented limitation of ABI testing 1, 2
• Do not wait for symptoms to develop before pursuing further evaluation, as asymptomatic PAD still carries significant cardiovascular risk 1
• Do not assume symmetry – PAD progression is often asymmetric between limbs, as your results demonstrate 6
• Avoid relying on a single TBI measurement – obtain repeat measurements to confirm the finding, particularly given the borderline nature of your right TBI 5

Bottom Line

Your right TBI of 0.77, while only mildly reduced, represents a meaningful discrepancy from your left side and indicates early arterial disease that your normal ABI failed to detect. This warrants vascular imaging to define the anatomy and severity of disease, initiation of preventive medical therapy, and ongoing surveillance. 1, 4, 3