• Measurement of the ankle-brachial index (ABI) is the primary method for establishing the diagnosis of PAD. An ABI of ≤0.90 has been demonstrated to have high sensitivity and specificity for the identification of PAD compared with the gold standard of invasive arteriography.
• The incremental value of ABI beyond standard risk scores (e.g, Framingham) in predicting future death and cardiovascular events has been established by epidemiologic studies. An ABI <0.9 or >1.4 portends an increased risk of major cardiovascular events.
• In the setting of compelling symptoms and normal results on noninvasive vascular testing at rest, obtaining an ABI with exercise can be helpful. A drop in the ABI to a value ≤0.9 is indicative of a hemodynamically significant arterial obstruction. Other more specific criteria include a drop of 30 mm Hg or 20% of the baseline ABI with exercise, and a delayed (>3 minutes) recovery.
• After a patient is identified with symptoms consistent with IC and an abnormal ABI, it is important to rule out other potential etiologies that can mimic PAD symptoms. The differential diagnosis for IC is extensive and is summarized in Table I.
• Perhaps worthy of special mention is the differentiation of neurogenic claudication from vasculogenic claudication, because this is the most common clinical diagnostic challenge.
  • Neurogenic claudication most often occurs secondary to nerve root compression on exit from the spinal canal. These symptoms may often include lower extremity pain that is radiating in nature, starting at the hips or buttocks and extending down the affected leg. In addition, radicular pain is frequently brought on by simple weight bearing or changes in posture (e.g., rising after prolonged sitting) and relieved by a change in position to relieve the load on the spine (e.g, lumbar flexion, sitting down).
  • Vasculogenic claudication is often induced by leg exercise and quickly relieved by rest (resulting in a decrease in muscular metabolic requirement), without a need to change position.
• Additional imaging modalities that can more precisely localize arterial lesions - arterial duplex, computed tomography angiography (CTA), magnetic resonance (MR) angiography (MRA), and contrast arteriographydshould be reserved for patients in whom revascularization treatment is being considered.