More questions for an old vascular test
I was at a wound care conference several weeks ago and got into a conversation with a colleague regarding ABI testing. ABI stands for ankle brachial index, sometimes also called an ankle brachial pressure index or ABPI. An ABI is used to ascertain and quantify blood flow to the foot. For years, ABI testing was the gold standard to determine flow to the foot. But as newer, more sophisticated testing becomes available, some doctors are questioning the validity of the ABI.
What is ABI testing?
The ABI test is relatively simple and cost-effective to perform. Using a blood pressure cuff and handheld Doppler device, the systolic blood pressure of the arm (brachial artery) is divided by the systolic blood pressure in the foot (posterior tibial or anterior tibial artery). The resulting ratio in a healthy patient would be 120/120 or 1.0. As occlusion due to peripheral arterial disease (PAD) occurs in the lower extremity, the ratio starts to drop. For instance, a brachial BP of 120 mm/hg and posterior tibial pressure of 140 mm/hg results in a ratio of 0.85. This ratio would indicate lower extremity peripheral arterial disease.
Which arteries to use in ABI testing?
My question to my colleague was this: which of the two primary arteries in the foot do we measure? There's only one brachial artery in the arm but there are two arteries in the foot. Which artery is the right one to measure?
I spoke with the vascular techs in both of the hospitals where I work and both said they didn't know. The first said she does not do the calculations and leaves that up to the doc. The second said that she had a machine that figured that out. That left me with one bigger question. Thirty years of practice and why don't I have an answer to this simple question. If we look at medicine as a mature science, how come we don't have this simple answer.
A search on the internet pulled a peer-reviewed article that stated the proper artery to use was the artery with the highest pressure. (1) That didn't make sense in the least. What if the other artery is totally occluded.
A little more searching found that there are others with this same question about ABI testing. McDermott et al had an interesting article that recommended averaging the two arteries of the foot. (2) Al-Qaisi et al agreed that although we still rely on the ABI as a workhorse in the vascular lab, there needs to be standardization of the test. (3)
I'll still rely on the ABI to help determine a general sense of PAD, whether or not to use compression therapy for wounds and to determine the appropriate level of amputation. But now I'll combine those tests more with trans-cutaneous oxygen testing and when possible, arteriograms.
1. Vowden P, Vowden K (March 2001). "Doppler assessment and ABPI: Interpretation in the management of leg ulceration". Worldwide Wounds.
2. McDermott M, Criqui M, Kiang L, Guralnik J, Greenland P, Martine G, Pearce W (2000) "Lower ankle/brachial index, as calculated by averaging the dorsalis pedis and posterior tibial arteries, associated with leg functioning in peripheral arterial disease" Journal of Vascular Surgery 32:6 1164-1171
3. Al-Qaisi, M; Nott, DM; King, DH; Kaddoura, S (2009). "Ankle brachial pressure index (ABPI): An update for practitioners" Vascular Health and Risk Management. 5: 833–41.