What's the next step for an older adult patient with an ankle-brachial index (ABI) of 0.9 to 1.1, possibly with a history of smoking, diabetes, hypertension, or hyperlipidemia?

Management of Ankle-Brachial Index 0.9 to 1.1

Patients with an ABI of 0.9 to 1.1 fall into the "borderline" cardiovascular risk category and require further vascular evaluation with exercise treadmill ABI testing if they have exertional leg symptoms, or cardiovascular risk factor optimization and clinical surveillance if asymptomatic. 1

Understanding the ABI Range 0.9-1.1

The ABI range of 0.9 to 1.1 encompasses two distinct categories with different clinical implications:

• ABI 0.91-0.99 is classified as "borderline" and indicates patients who warrant further evaluation for subclinical peripheral artery disease (PAD) and increased cardiovascular risk 1
• ABI 1.00-1.10 is within the normal range (1.00-1.40), though the optimal cardiovascular risk profile occurs at ABI 1.11-1.40 2
• ABI exactly 0.90 is the diagnostic threshold for PAD, so values at or just above this cutoff require careful clinical interpretation 1

Immediate Next Steps Based on Symptoms

For Patients with Exertional Leg Symptoms

Proceed immediately to exercise treadmill ABI testing, as a normal or borderline resting ABI does not exclude hemodynamically significant PAD in symptomatic patients 1, 3:

• Exercise testing is a Class I, Level B-NR recommendation for patients with exertional non-joint-related leg symptoms and ABI 0.91-1.40 1
• A post-exercise ankle pressure decrease >30 mmHg or ABI decrease >20% confirms PAD even when resting ABI appears normal 1, 3
• Isolated iliac artery disease commonly presents with normal resting ABI but becomes apparent with exercise stress 3

For Asymptomatic Patients with ABI 0.91-0.99 (Borderline)

These patients require aggressive cardiovascular risk factor modification and consideration for additional vascular testing 1:

• Borderline ABI (0.91-0.99) identifies patients at increased cardiovascular risk who warrant "further evaluation" per Class IIa, Level A evidence 1
• Consider exercise ABI testing even in asymptomatic patients with borderline values and multiple cardiovascular risk factors 1
• Measure ABI in both legs, as using the lower ABI identifies more at-risk individuals 1, 4

For Asymptomatic Patients with ABI 1.00-1.10 (Normal)

Focus on cardiovascular risk factor optimization and clinical surveillance:

• These patients have lower cardiovascular risk than those with abnormal ABI, but still require standard preventive care 2
• No additional vascular testing is indicated unless symptoms develop 1

Special Considerations for High-Risk Populations

Diabetic Patients

Exercise extreme caution interpreting ABI in diabetic patients, as arterial calcification frequently produces falsely normal or elevated readings despite significant ischemia 1, 3, 5:

• ABI sensitivity is significantly reduced in diabetic patients, particularly with neuropathy or chronic kidney disease 3, 5
• If ABI is 0.9-1.1 in a diabetic patient with any foot symptoms, non-healing wounds, or absent pulses, immediately obtain toe-brachial index (TBI) 1
• TBI <0.70-0.75 confirms PAD when ABI is unreliable 1
• Up to 50% of diabetic foot ulcer patients have coexisting PAD that may be masked by normal ABI 3

Patients with Smoking History, Hypertension, or Hyperlipidemia

These patients warrant more aggressive surveillance even with borderline ABI 1, 6:

• Age ≥65 years, smoking history, or diabetes are independent indications for ABI screening 1
• Borderline ABI in the presence of multiple risk factors should prompt consideration of exercise testing 1

Cardiovascular Risk Stratification and Management

Risk Factor Optimization (All Patients with ABI 0.9-1.1)

Implement aggressive cardiovascular risk reduction regardless of PAD symptoms 1, 6:

• Statin therapy: Target LDL-C <1.4 mmol/L (<55 mg/dL) or ≥50% reduction for patients with diabetes and borderline ABI (Class I, Level B evidence) 1
• Antiplatelet therapy: Consider aspirin 100 mg daily for patients with borderline ABI and multiple cardiovascular risk factors 1
• Smoking cessation: Mandatory counseling and pharmacotherapy for all current smokers 1
• Blood pressure control: Treat hypertension to guideline targets 1
• Glycemic control: Optimize diabetes management if present 1

Dual Antiplatelet Therapy Consideration

For patients with symptomatic PAD confirmed by exercise testing and without high bleeding risk, consider combination therapy 1:

• Low-dose rivaroxaban 2.5 mg twice daily plus aspirin 100 mg daily is a Class IIa, Level B recommendation for chronic symptomatic PAD 1
• This applies only after PAD is confirmed and bleeding risk is assessed 1

Common Clinical Pitfalls to Avoid

Never assume PAD is absent based solely on a single resting ABI measurement in the 0.9-1.1 range if the patient has exertional leg symptoms 1, 3:

• Resting ABI has insufficient sensitivity to exclude PAD in symptomatic patients 3
• Exercise testing is mandatory to unmask moderate stenoses 1

Never rely on ABI alone in diabetic patients without also assessing TBI or obtaining Doppler waveforms 1, 3, 5:

• Medial arterial calcification causes falsely reassuring ABI readings in up to 50% of diabetic patients with PAD 3, 5
• Even skilled examiners can palpate pulses despite significant ischemia 3

Never use a single-leg ABI measurement for risk stratification 1, 4:

• Always measure bilateral ABI and use the lower value for cardiovascular risk assessment 1
• Using the higher ABI overlooks patients at high risk for cardiovascular events 4

Never delay exercise testing in symptomatic patients while waiting for symptoms to worsen 1:

• Early diagnosis allows for timely intervention and risk factor modification 1
• PAD progression increases amputation and cardiovascular event risk 6

Follow-Up and Monitoring

Establish a surveillance protocol based on initial findings:

• Repeat ABI annually for patients with borderline values (0.91-0.99) and cardiovascular risk factors 1
• Immediate vascular referral if exercise ABI confirms PAD or if symptoms progress 1
• Serial ABI measurements improve diagnostic accuracy over single measurements 2