What is the interpretation of the Ankle-Brachial Index (ABI) and recommended management for a patient with elevated ankle blood pressure, painful varicose veins, and hypertension?

Ankle-Brachial Index Calculation and Interpretation

This patient has an abnormally elevated ABI of 1.38, indicating non-compressible arteries from medial arterial calcification, which requires toe-brachial index (TBI) measurement to accurately assess for peripheral arterial disease. 1

ABI Calculation

Using the standard formula per ACC/AHA guidelines 1:

• Numerator: Higher ankle pressure = 170 mmHg (using the higher of the two ankle readings)
• Denominator: Higher brachial pressure = 123 mmHg
• ABI = 170/123 = 1.38

Interpretation of Results

ABI >1.40 Indicates Non-Compressible Arteries

• Your patient's ABI of 1.38 approaches the threshold of 1.40, which indicates arterial stiffness from medial arterial calcification 1
• An ABI >1.40 has 99% specificity but renders the test unreliable for detecting PAD because calcified vessels resist compression, artificially elevating pressure readings 1
• The normal ABI range is 0.91-1.40; values >1.40 are considered non-compressible 1

Clinical Significance of Painful Varicose Veins

• The patient's symptoms (painful varicose veins worse with ambulation and at rest) are not typical of PAD, which classically presents as intermittent claudication (pain with walking that resolves with rest) 1
• However, the elevated ankle pressures suggest underlying arterial pathology that must be evaluated further 2

Mandatory Next Step: Toe-Brachial Index Measurement

When ABI >1.40 (or approaching this threshold), toe pressure with waveforms must be obtained because medial arterial calcification makes ankle arteries stiff and resistant to compression, artificially elevating pressure readings and masking true PAD. 2

TBI Interpretation Thresholds

• Normal TBI: ≥0.70 1, 2
• Abnormal TBI: <0.70 (indicates PAD) 1, 2
• Critical ischemia: Toe pressure <30 mmHg (requires urgent vascular evaluation) 2

Why TBI is Essential in This Case

• Toe arteries are less susceptible to medial calcification than ankle arteries, providing more accurate assessment 2
• The ABI has reduced sensitivity in patients with arterial calcification, with sensitivity dropping to 15-79% in some populations 3, 4
• Using ABI alone when >1.40 will miss significant PAD in patients with calcified vessels 5, 6

Additional Diagnostic Considerations

Adjunctive Testing Options

• Doppler waveforms and/or pulse volume recordings (PVR) at the ankle can confirm concordance with the presence and severity of PAD and suggest non-compressible arteries 1
• Duplex ultrasound provides anatomic and hemodynamic information with 85-90% sensitivity and >95% specificity for stenosis >50% 7

Common Pitfall to Avoid

• Do not rely on ABI alone when values approach or exceed 1.40 - this is the most critical error in patients with suspected arterial calcification 2
• The elevated ankle pressures may be masking significant PAD that would be detected by TBI 5, 6

Management Algorithm

1. Order toe-brachial index with waveforms immediately (Class I recommendation) 2
2. If TBI <0.70: Diagnose PAD and initiate guideline-directed medical therapy 1
3. If TBI ≥0.70: Consider alternative diagnoses for leg symptoms (venous insufficiency is likely given varicose veins) 1
4. If toe pressure <30 mmHg: Urgent vascular surgery referral for potential revascularization 2

Addressing the Varicose Veins

• The painful varicose veins with symptoms at rest and with ambulation are more consistent with venous insufficiency rather than arterial disease 1
• However, arterial disease must be definitively ruled out with TBI before pursuing venous interventions 2