When is an Ankle-Brachial Index (ABI) Not Appropriate?
The Ankle-Brachial Index (ABI) is not appropriate in patients who are not at increased risk of peripheral artery disease (PAD) and without history or physical examination findings suggestive of PAD. 1
Situations Where ABI is Not Appropriate
Patients without risk factors for PAD - In individuals without risk factors for atherosclerosis and who are <50 years of age, the prevalence of PAD is very low (approximately 1%), making routine ABI testing unnecessary 1
Asymptomatic patients without risk factors - The yield of ABI testing among younger, asymptomatic individuals without risk factors for atherosclerosis is low, and these patients should not be routinely tested for PAD 1
Patients with noncompressible arteries - When ABI values are >1.40, indicating noncompressible vessels (common in patients with diabetes mellitus and advanced chronic kidney disease), the ABI is not appropriate and alternative testing should be used 1
Anatomic assessment in asymptomatic PAD - Invasive and noninvasive angiography (CTA, MRA) should not be performed for anatomic assessment in patients with asymptomatic PAD 1
Alternative Tests When ABI is Not Appropriate
Toe-Brachial Index (TBI) - Should be measured to diagnose patients with suspected PAD when the ABI is >1.40 due to noncompressible arteries 1
Doppler waveform analysis - Can detect PAD even when ABI values are falsely normal due to arterial calcification 2
Pulse volume recordings (PVRs) - Useful in patients with noncompressible vessels, as this modality relies on limb volume change rather than the pressure required to impede flow 1
Transcutaneous oxygen pressure (TcPO2) - Can be used to evaluate local perfusion in patients with noncompressible arteries 1
Skin perfusion pressure (SPP) - Useful for evaluating local perfusion in patients with noncompressible arteries 1
Plantar Acceleration Time - A newer technique that demonstrates high correlation with ABI in patients with compressible arteries and may be suitable for patients with noncompressible arteries 3
Clinical Implications of Noncompressible Arteries
Patients with noncompressible arteries (ABI >1.40) have significantly higher rates of cardiovascular mortality (21.7%) compared to those with normal ABI (0%) at 2 years follow-up 4
All-cause mortality is also significantly higher in patients with noncompressible arteries (42%) compared to those with normal ABI (14%) 4
These findings emphasize the importance of using alternative diagnostic methods when ABI is not appropriate due to noncompressible arteries 4
Discordant ABI Values
Patients with discordant ABI results (normal overall ABI but abnormal when calculated using one of the other ankle artery pressures) have increased risk of myocardial infarction (HR 1.31), ischemic stroke (HR 1.53), and all-cause mortality (HR 1.27) 5
Clinicians should examine ABI calculations using all four ankle arteries to better characterize cardiovascular risk 5
Diagnostic Accuracy Considerations
ABI has moderate predictive value in diagnosing lower extremity arterial disease, with sensitivity of 72.3% and specificity of 69.3% when compared to duplex ultrasound 6
Normal range ABI outcomes cannot be taken to infer the absence of lower extremity arterial disease, and further arterial imaging should be considered in those with suspected underlying disease requiring intervention 6