What test should be ordered when foot pulses are non-palpable?

From the Guidelines

When foot pulses are non-palpable, an ankle-brachial index (ABI) test should be ordered as the initial diagnostic assessment. This non-invasive test compares blood pressure measurements in the ankles to those in the arms to evaluate blood flow and detect peripheral artery disease (PAD) 1. The ABI test is a simple, reliable, and non-invasive procedure that can be performed at the bedside using sphygmomanometers and a hand-held Doppler machine 1. If the ABI is abnormal (typically less than 0.9) or if clinical suspicion remains high despite normal ABI results, further vascular imaging should be considered, such as duplex ultrasound, CT angiography, or MR angiography 1. These tests provide detailed information about arterial blood flow, vessel patency, and the location and severity of any blockages. Non-palpable foot pulses often indicate compromised arterial circulation, which may be due to atherosclerosis, embolism, or other vascular pathologies. Prompt diagnosis is essential as PAD increases risk for limb ischemia, tissue loss, and cardiovascular events. Patients with non-palpable pulses should also undergo comprehensive cardiovascular risk assessment, as peripheral vascular disease often coexists with coronary and cerebrovascular disease.

Some key points to consider when interpreting ABI results include:

• An ABI <0.90 should be considered the threshold for confirming the diagnosis of lower-extremity PAD 1
• The ABI should be reported as abnormal (ABI ≤0.90), borderline (ABI 0.91-0.99), normal (ABI 1.00-1.40), or noncompressible (ABI >1.40) 1
• In patients with suspected PAD, toe pressure/toe-brachial index (TBI) with waveforms should be performed when the resting ABI is >1.40 (noncompressible) 1
• Patients with suspected chronic symptomatic PAD and normal or borderline resting ABI (>0.90 and ≤1.40, respectively) should undergo exercise treadmill ABI testing to evaluate for PAD 1

It is also important to note that the absence of pedal pulses suggests PAD, but this method of assessment of arterial perfusion is often unreliable, especially in persons with diabetes 1. Therefore, the ABI test is a more reliable and accurate method for diagnosing PAD in these patients.

In addition to the ABI test, other diagnostic tests such as measurements of toe pressure or transcutaneous pressure of oxygen (TcPo2) may be useful in certain situations, such as when the ABI is noncompressible or when there is a high clinical suspicion of PAD despite a normal ABI result 1. However, the ABI test remains the cornerstone for initial diagnosis of PAD, and further testing should be guided by the results of the ABI test and the clinical presentation of the patient.

From the Research

Tests for Non-Palpable Foot Pulses

When foot pulses are non-palpable, it is essential to order tests that can accurately diagnose peripheral arterial disease (PAD). The following are some of the tests that can be ordered:

• Ankle-Brachial Index (ABI) test: This is a simple, non-invasive test that measures the ratio of blood pressure in the ankles to the blood pressure in the arms 2, 3, 4.
• Doppler ultrasound: This test uses sound waves to create images of the blood vessels and can help diagnose PAD 5.
• Ankle Doppler for Cuffless Ankle Brachial Index Estimation: This is a new method that uses handheld Doppler waveforms to estimate the ABI without the need for compression 5.

Advantages and Limitations of Each Test

Each test has its advantages and limitations:

• ABI test: This test is simple, inexpensive, and widely available, but it may not be accurate in patients with diabetes or those with severe PAD 2, 4.
• Doppler ultrasound: This test is more accurate than the ABI test, but it requires specialized equipment and training 5.
• Ankle Doppler for Cuffless Ankle Brachial Index Estimation: This test is non-invasive, easy to use, and can be performed without compression, but more research is needed to confirm its accuracy 5.

Clinical Implications

The choice of test depends on the clinical presentation and the availability of resources. A thorough physical examination, including the palpation of foot pulses and the auscultation of femoral bruits, can also help diagnose PAD 2. The emphasis should be on encouraging a thorough physical examination and using the ABI test or other non-invasive tests to confirm the diagnosis. Alternative approaches, such as a blood test for PAD, may also be considered to improve diagnostic simplicity and efficiency 6.