What test should be ordered now for a 58‑year‑old woman with hypertension, hyperlipidemia, mild chronic obstructive pulmonary disease (COPD) on atorvastatin, olmesartan, tiotropium, and albuterol as needed, who has progressive calf pain after walking more than two blocks for four months, diminished dorsalis pedis and posterior tibial pulses bilaterally, normal femoral and popliteal pulses, and a resting ankle‑brachial index (ABI) of 1.1 on the right and 0.94 on the left?

Exercise Ankle-Brachial Index

You should order an exercise ankle-brachial index (option b) for this patient with classic intermittent claudication symptoms and borderline resting ABI values.

Clinical Reasoning

This 58-year-old woman presents with classic intermittent claudication—progressive calf pain and cramping after walking more than two blocks that resolves with rest—combined with diminished distal pulses and borderline resting ABI values (1.1 right, 0.94 left). 1

Why Resting ABI Is Insufficient Here

• The left ABI of 0.94 falls in the borderline zone (0.91–1.00), where clinical judgment is essential and the diagnosis of PAD cannot be definitively excluded. 1
• The right ABI of 1.1 is normal at rest, yet the patient has bilateral symptoms, indicating that resting measurements may not capture exercise-induced ischemia. 1
• Resting ABI sensitivity increases significantly when measured immediately after treadmill exercise, making post-exercise ABI the appropriate next step when resting values are borderline but symptoms are classic for claudication. 1

Exercise ABI Diagnostic Value

• With leg exercise, ankle pressure decreases more in patients with even moderate occlusive PAD compared to healthy individuals, and recovery time is prolonged proportional to disease severity. 1
• In patients with classic intermittent claudication and borderline resting ABI, exercise testing unmasks hemodynamically significant stenoses that are compensated at rest but become symptomatic with increased metabolic demand. 1
• A post-exercise ABI drop of ≥20% or an absolute decrease of ≥0.15 confirms exercise-induced arterial insufficiency and establishes the diagnosis of PAD. 1

Why Not the Other Options

CT Angiography (Option a)

• CTA is rated highly (7–8) by the American College of Radiology for acute limb ischemia or when planning revascularization, not for initial diagnostic confirmation in stable claudication with borderline ABI. 1
• This patient has no acute presentation—no rest pain, no tissue loss, no cool extremities, and normal coloration—making anatomic imaging premature before confirming hemodynamically significant disease. 1, 2
• The ACR appropriateness criteria for claudication assessment recommend noninvasive hemodynamic testing first (ABI rated 9, exercise testing implied), with anatomic imaging reserved for revascularization planning. 1

Toe-Brachial Index (Option c)

• TBI is indicated when ABI >1.40 (non-compressible vessels from medial arterial calcification), not when ABI is in the normal-to-borderline range. 1, 2
• This patient's ABIs are 1.1 and 0.94—both compressible—so TBI adds no diagnostic value over exercise ABI testing. 1
• TBI is most useful in diabetic patients or those with chronic kidney disease where vessel calcification is common; this patient has neither documented diabetes nor CKD. 1, 2

Clinical Context Supporting Exercise Testing

• Both the sensitivity and specificity of ABI <0.9 is about 95% for detecting angiographic arterial disease, but values between 0.91–1.00 require clinical correlation and often exercise provocation. 1
• The ACR rates "risk factor analysis, lipid profile, and ABIs" as 9 (usually appropriate) for initial claudication evaluation, with exercise testing the logical next step when resting ABI is equivocal. 1
• Her symptoms are functionally limiting (cannot walk >2 blocks for 4 months), meeting the threshold where confirming PAD will guide medical management including supervised exercise therapy, antiplatelet therapy, and risk factor optimization. 1

Management After Positive Exercise ABI

Once exercise ABI confirms PAD:

• Best medical management including supervised exercise program is rated 9 (usually appropriate) for mild-to-moderate claudication. 1
• Antiplatelet therapy (aspirin or clopidogrel) is rated 7–8 to reduce cardiovascular events. 1
• Continue atorvastatin and optimize blood pressure control (already on olmesartan). 1
• Anatomic imaging (CTA, MRA, or duplex ultrasound) becomes appropriate only if symptoms remain functionally limiting despite 3–6 months of optimal medical therapy and supervised exercise, at which point revascularization planning may be considered. 1

Common Pitfalls to Avoid

• Do not proceed directly to anatomic imaging without confirming hemodynamically significant PAD in patients with borderline resting ABI—this leads to unnecessary radiation, contrast exposure, and potential overtreatment. 1
• Do not dismiss claudication symptoms when resting ABI is >0.90; up to 20% of patients with PAD have normal resting ABI but abnormal exercise ABI. 1
• Do not confuse this stable, chronic presentation with acute limb ischemia, which would require immediate anticoagulation and urgent CTA. 2, 3