What are the indications and interpretation of Ankle-Brachial Index (ABI) screening in patients over 65 years old with a history of smoking, diabetes, high blood pressure, or high cholesterol?

ABI Screening: Indications and Interpretation

Who Should Be Screened

All patients ≥65 years old should undergo ABI screening, regardless of symptoms, and this indication is strengthened by the presence of cardiovascular risk factors including smoking, diabetes, hypertension, or hyperlipidemia. 1

• Age ≥65 years alone is sufficient to warrant ABI screening according to ACC/AHA guidelines, with the 2011 focused update lowering the threshold from 70 to 65 years based on epidemiologic data showing 21% prevalence of PAD in this age group. 1

• Patients aged 50-64 years should be screened if they have a history of smoking OR diabetes, as these two risk factors show the strongest association with PAD development. 1

• The combination of multiple risk factors (smoking, diabetes, hypertension, hyperlipidemia) in your patient population substantially increases PAD prevalence and justifies screening even more strongly. 2, 3

• Note that the U.S. Preventive Services Task Force recommends against routine screening in asymptomatic adults, citing insufficient evidence that screening improves cardiovascular outcomes; however, ACC/AHA guidelines take precedence for cardiovascular disease management and emphasize the value of risk stratification. 1, 2

How to Perform ABI Measurement

Obtain resting systolic blood pressures at both brachial arteries and both ankle arteries (dorsalis pedis and posterior tibial) using a handheld Doppler device with the patient supine. 2, 4

• Calculate ABI for each leg by dividing the higher ankle pressure (between dorsalis pedis and posterior tibial) by the higher arm pressure. 4

• Measure blood pressure in both arms initially to detect inter-arm differences >15-20 mmHg, which suggests subclavian stenosis and requires using the higher arm pressure for calculations. 4

• The ABI should be measured in both legs to confirm diagnosis and establish baseline values. 1

Interpretation of ABI Results

ABI values should be categorized as: ≤0.90 (abnormal/PAD present), 0.91-0.99 (borderline), 1.00-1.40 (normal), or >1.40 (noncompressible vessels). 1, 2

ABI ≤0.90 (Abnormal)

• Diagnostic for PAD with 80% sensitivity and 95% specificity, confirming the diagnosis without need for additional testing. 5, 6
• Associated with a 2-4 fold increase in cardiovascular events and all-cause mortality. 6

ABI 0.91-0.99 (Borderline)

• Represents borderline PAD and warrants close monitoring. 1
• Consider exercise treadmill ABI testing if the patient develops exertional leg symptoms, as post-exercise ABI may unmask PAD not evident at rest. 2, 7

ABI 1.00-1.40 (Normal)

• Normal range, but repeat screening every 2-3 years in high-risk patients given their cardiovascular risk profile. 2

ABI >1.40 (Noncompressible)

• Indicates falsely elevated values due to arterial calcification, most commonly seen in patients with long-standing diabetes or advanced age. 1, 5
• Requires toe-brachial index (TBI) measurement as the alternative diagnostic test, with TBI <0.70 diagnostic for PAD. 1, 2

Clinical Management Based on Results

If ABI ≤0.90 (PAD Confirmed)

Reclassify the patient to very high cardiovascular risk and initiate aggressive medical management immediately. 2, 5

• Smoking cessation is mandatory and should be treated more aggressively than in other cardiovascular conditions. 1, 2
• High-intensity statin therapy regardless of baseline LDL cholesterol. 2, 7
• Antiplatelet therapy with aspirin or clopidogrel for secondary prevention. 2, 7
• Blood pressure control to target <130/80 mmHg using ACE inhibitors or ARBs preferentially. 8, 7
• Diabetes management with HbA1c target <7.0% if applicable. 8

If ABI 0.91-0.99 (Borderline)

• Intensive cardiovascular risk factor modification is warranted even though PAD is not definitively diagnosed. 2
• Monitor for development of symptoms and consider exercise ABI testing if claudication develops. 2

If ABI 1.00-1.40 (Normal)

• Continue aggressive cardiovascular risk factor management given the patient's high-risk profile (age >65 with multiple risk factors). 2
• Reassess clinically every year and repeat ABI every 2-3 years. 2

If ABI >1.40 (Noncompressible)

• Proceed directly to toe-brachial index measurement without delay, as this is particularly common in diabetic patients. 1, 5
• If TBI <0.70, manage as confirmed PAD with aggressive risk factor modification. 2

Important Clinical Caveats

• Classic claudication is present in only 10-11% of PAD patients; 40-50% are completely asymptomatic and another 40-50% have atypical leg symptoms, so absence of symptoms does not exclude PAD. 6, 9, 7

• Physician awareness of PAD diagnosis is poor (49% in one large study), leading to undertreatment compared to coronary artery disease, despite similar cardiovascular risk. 9

• In diabetic elderly patients (>70 years), PAD prevalence reaches 71% when ABI is systematically measured, far higher than clinical diagnosis alone would suggest. 8

• The presence of three or more cardiovascular risk factors confers a 10-fold increase in PAD risk, making your patient population particularly high-yield for screening. 7