Resting ABI Without Exercise is the Appropriate Initial Test
For an elderly patient with suspected vascular disease, order a resting Doppler ankle-brachial index (ABI) with measurement of both brachial pressures and left ankle pressures (posterior tibial and dorsalis pedis arteries) WITHOUT exercise as the initial diagnostic test. 1
Why Start with Resting ABI
The resting ABI is the Class I, Level B recommendation as the initial diagnostic test for peripheral arterial disease (PAD) and may be the only test required to establish diagnosis and institute guideline-directed medical therapy. 1
The resting ABI has sensitivity of 69-79% and specificity of 83-99% compared with imaging studies showing significant arterial stenoses in symptomatic patients. 1
It is noninvasive, simple to perform, has minimal risks, and is suitable as both a screening and diagnostic test. 1
When to Add Exercise Testing
Exercise ABI testing is not part of the initial diagnostic workup but is reserved for specific clinical scenarios:
If the resting ABI is normal (1.00-1.40) or borderline (0.91-0.99) BUT the patient has symptoms suggestive of claudication, then exercise treadmill ABI testing should be performed. 1, 2
Exercise testing objectively measures functional limitations and enhances sensitivity for PAD detection when resting values don't explain symptoms. 1
Research demonstrates that among symptomatic patients with normal resting ABI who underwent exercise testing, 31% had their ABI fall below 0.9 after exercise, revealing previously undetected PAD. 2
Critical Interpretation Points
Report results using standardized criteria: 1
- Abnormal: ABI ≤0.90 (confirms PAD diagnosis)
- Borderline: ABI 0.91-0.99 (requires clinical context)
- Normal: ABI 1.00-1.40
- Noncompressible: ABI >1.40 (suggests arterial calcification)
Special Considerations for Elderly Patients
If ABI >1.40 (noncompressible vessels), which is common in elderly patients with diabetes or chronic kidney disease, measure toe-brachial index (TBI) instead. 1
Digital arteries are rarely noncompressible, making TBI reliable when ABI is falsely elevated. 1
A TBI ≤0.70 is abnormal and confirms PAD diagnosis. 1
Adjunctive Testing to Consider with Resting ABI
Segmental pressures with pulse volume recordings (PVR) and/or Doppler waveforms are Class IIa recommendations that can be performed alongside the resting ABI to: 1
- Localize anatomic segments of disease (aortoiliac, femoropopliteal, infrapopliteal)
- Confirm concordance with PAD presence and severity
- Identify noncompressible arteries when there's discordance
Common Pitfalls to Avoid
Do not routinely order exercise ABI as the initial test - it is reserved for when resting ABI is normal/borderline but symptoms persist. 1
Measure blood pressure in both arms - an inter-arm difference >15-20 mmHg suggests subclavian stenosis and affects ABI accuracy. 1
Use the higher of the two ankle pressures (dorsalis pedis or posterior tibial) for diagnostic purposes to minimize overdiagnosis, though some evidence suggests using the lower pressure identifies more at-risk patients. 3, 4
In elderly patients with potential calcification, don't assume a high ABI (>1.40) means no disease - proceed to TBI or imaging. 1
When Imaging Becomes Necessary
Anatomic imaging studies (duplex ultrasound, CTA, MRA, or catheter angiography) are generally reserved for: 1
- Highly symptomatic patients in whom revascularization is being considered
- When symptoms are functionally limiting and response to medical therapy is inadequate
- To assess anatomy and determine revascularization strategy
There is no better initial test than resting ABI for suspected PAD - it remains the gold standard first-line diagnostic tool recommended by all major guidelines. 1, 5