Choosing between a manual or automated ankle-brachial index (ABI) test

26th Feb 2021

Historically, ankle-brachial index (ABI) testing was always done manually, and still is at some sites. Now, automated ABI machines are available in many locations, and they have their benefits. Let’s cover a few differences between manual and automated ABIs so you can pick between the two and appreciate their advantages.

 

Advantages of manual ABIs 

Manual ABIs have three main advantages:

  • They are not hard to learn.
  • They are reliable.
  • They only need a blood pressure cuff with a pump and a Doppler pen.

Manual ABI tests are a great option when a machine isn’t available. But, a downside to a manual ABI is that you cannot print out a report to share.

Blood pressure cuff with pump and Doppler pen beside a list of manual ankle-brachial index (ABI) advantages. Illustration.

Figure 1. Advantages of a manual ankle-brachial index (ABI) include that they are easy to learn, are reliable, and only require a blood pressure cuff with a pump and a Doppler pen.

Most handheld, continuous-wave Doppler probes are 8–10 MHz. Medmastery note.

In fact, ABI ratios can be even be calculated without the use of a Doppler pen. In an emergency situation when an ABI machine or a Doppler pen is not available, you can simply grab a portable blood pressure (BP) machine. Put the cuff on each limb and take the patient’s systolic pressures to manually calculate the ABI ratios. 

This is less accurate because without the Doppler you will not hear the waveforms. Doppler waveforms are more sensitive and are typically faster at detecting the earliest pulse. However, blood pressure cuffs can give you a general idea if a disease is present—especially if you see a big drop between the arm and ankle, which is helpful in an emergency. 

Pro tip: start by taking blood pressure readings from the leg of concern. If the patient’s blood pressure cannot be detected in the leg of concern, you already know that blood flow is severely restricted. Try placing the blood pressure cuff’s artery marker over the dorsalis pedis artery (DPA) and then over the posterior tibial artery (PTA) and compare the two readings. Medmastery note.

If a manual ABI is performed, there is still the option of using an older photoplethysmography (PPG) portable recorder to perform digit PPG and toe-brachial index (TBI) testing. The results can be printed and scanned into the patient’s chart. 

Photoplethysmography (PPG) portable recorder. Illustration.

Figure 2. An older photoplethysmography (PPG) portable recorder can be used to perform digit PPGs and toe-brachial index (TBI) testing in conjunction with a manual ankle-brachial index (ABI).

 

Advantages of using an automated ABI machine

Of course, when one is available, an automated ABI machine has several advantages:

  • Automated protocols
  • Automated calculations
  • Ease of TBI testing
  • Ability to print / transfer a report with analog waveforms 

Illustration of an automated ankle-brachial index (ABI) machine beside a list of advantages.

Figure 3. Advantages of using an automated ankle-brachial index (ABI) machine include automated protocols, automated calculations, ease of toe-brachial index (TBI) testing, and the ability to print or transfer a report with analog waveforms. 

As you can see, an automated ABI machine may be preferable, but a manual ABI still provides information that is reliable and useful for diagnostic purposes.

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Recommended reading

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