What exactly is an ABI? ABI stands for Ankle Brachial Index. This is a non-invasive bedside tool that compares the systolic blood pressure of the ankle to that of the arm. It is done to rule out Peripheral Arterial Disease in the lower extremities. The ABI is considered the “bedside” gold standard diagnostic test and can be done by any trained clinician in a clinic, hospital, nursing home and/or even the home care setting. All you need is a blood pressure cuff and a hand held Doppler.
Why do we do the Ankle Brachial Index or ABI? Well, there are several reasons why we include the ABI as part of our assessment for the patient with lower extremity wounds. First of all, in order to heal a wound we have to be sure that our patient has adequate blood flow. The ABI will tell us if the patient has impaired arterial blood flow, and how significant that impairment is. We also need to know the amount of compression that we can safely apply to the venous patient, in general the lower the patients ABI reading, the lower the amount of compression that can be safely applied.
When do I need to do the ABI? Standards of care and Guidelines dictate when we should be doing the Ankle Brachial Index. Our current standard of practice states to do the ABI: Anytime a patient has a lower extremity ulcer, when foot pulses are not clearly palpable, prior to applying compression wraps / garments or when the lower extremity ulcer is no longer healing.
What does the ABI “number” mean? First we need to be aware that not everyone’s ABI is reliable, in fact patients with diabetes or end-stage renal disease may have incompressible vessels rendering a falsely high ABI score. For these patients we use another diagnostic test called the Toe Brachial Pressure Index (TBPI) instead of the ABI. For those with ABI readings, in general as the patients ABI score decreases, this signifies that the patient has arterial disease of the lower extremity, and poor blood flow. Any patient with an abnormal reading needs a referral to a vascular specialist. Bedside interpretations of the ABI that we use as wound clinicians are: 1.0 considered a normal reading, an ABI of 0.9 indicate more venous, 0.6-0.8 indicate a mixed etiology (venous and arterial) and less than or equal to 0.5 is indicative of arterial disease of the lower extremity.
We as wound care clinicians are held to certain standards of care and must follow those guidelines established by the experts. Performing the ABI on patients before applying compression and on patients with lower extremity ulcers is one of them. As wound clinicians we use the ABI and our clinical assessment to help guide us into determining what type of ulcer we are dealing with so we can make appropriate referrals and develop the best treatment plan for our patients. It’s a step we can’t afford to leave out; our patient’s limb may depend on it.