Diagnostic Testing for Suspected Peripheral Artery Disease
Order a resting ankle-brachial index (ABI) as the initial diagnostic test for any patient with suspected peripheral artery disease. 1, 2
Initial Testing: Resting ABI
- Measure bilateral arm blood pressures and ankle pressures (posterior tibial and dorsalis pedis arteries) with the patient supine after 5-10 minutes of rest using a Doppler device 1
- Calculate ABI for each leg by dividing the higher ankle pressure by the higher brachial pressure 1, 2
- Interpret results as follows 1, 3:
- ABI ≤0.90: Abnormal, confirms PAD diagnosis
- ABI 0.91-0.99: Borderline
- ABI 1.00-1.40: Normal
- ABI >1.40: Non-compressible arteries (proceed to alternative testing below)
The resting ABI has 68-84% sensitivity and 84-99% specificity for PAD diagnosis, making it the cornerstone screening tool 1, 2. However, nearly half of symptomatic patients may have normal resting ABI values 4, 5, particularly those with diabetes or chronic kidney disease where sensitivity drops to 51% and 43% respectively 5.
When Resting ABI is Normal or Borderline BUT Symptoms Persist
Order exercise treadmill ABI testing to unmask flow-limiting stenosis 1, 2, 4:
- A post-exercise ankle pressure decrease >30 mmHg or ABI decrease >20% confirms PAD 2
- Exercise testing reveals PAD in 31% of symptomatic patients with normal resting ABI 4
When ABI is >1.40 (Non-compressible Arteries)
Order toe-brachial index (TBI) with toe pressures as the primary alternative test 1, 3, 2:
- Place cuffs on upper arms and photoplethysmography probe on distal pulp of first or second toe 1
- TBI ≤0.70 is abnormal and diagnostic of PAD 1, 3
- TBI has 85% sensitivity and 75% overall accuracy for detecting significant stenosis, even in patients with diabetes and CKD 6, 5
Common pitfall: Non-compressible arteries occur in 13-20% of patients, particularly those with diabetes or advanced chronic kidney disease 4, 5. These patients have significantly higher cardiovascular mortality (21.7% at 2 years) 7, so identifying them is critical.
Additional Laboratory Testing
Order the following blood tests for comprehensive cardiovascular risk assessment 1:
- Lipid profile including lipoprotein(a) (at least once in lifetime)
- Fasting glucose and HbA1c
- Renal function and electrolytes
- Complete blood count
- Coagulation studies
- Liver function tests
- Inflammatory markers (CRP and ESR)
Anatomic Imaging (Only When Considering Revascularization)
Do NOT order anatomic imaging for asymptomatic PAD or for initial diagnosis 3, 2. Reserve imaging for symptomatic patients being considered for intervention 1:
- Duplex ultrasound: First-line imaging with 85-90% sensitivity and >95% specificity for detecting >50% stenosis 3, 2
- CTA or MRA: For detailed anatomic characterization when planning revascularization 1, 3
- Catheter angiography: Reserved for patients with critical limb-threatening ischemia undergoing revascularization 1, 3
For Chronic Limb-Threatening Ischemia
Add perfusion assessment tests 1, 3:
- Toe pressure <30 mmHg confirms CLTI
- Transcutaneous oxygen pressure (TcPO2) <30 mmHg confirms CLTI
- Ankle pressure <50 mmHg confirms CLTI
Critical caveat: Physical examination alone is insufficient—objective testing is mandatory to confirm PAD diagnosis 2. In symptomatic patients with normal resting ABI, proceed directly to exercise testing or consider TBI rather than dismissing the diagnosis 4, 5.