Ankle-Brachial index
Editors-In-Chief: C. Michael Gibson, M.S., M.D., Alexandra Almonacid M.D., Jeffrey J. Popma M.D.
Synonyms and keywords: ABI, ankle brachial index
Overview
The Ankle Brachial Pressure Index (ABPI) is a measure of the fall in blood pressure in the arteries supplying the legs and as such is used to detect evidence of blockages (peripheral vascular disease). It is calculated by dividing the systolic blood pressure in the ankle by the higher of the two systolic blood pressures in the arms.
The pressures in the posterior tibial artery and dorsalis pedis artery in the feet and the brachial artery at the elbow are estimated. A Doppler probe is used, through a device called the Pulse Volume Recorder (some variances may apply depending on the physician), to monitor the pulse while a sphygmomanometer (blood pressure cuff) is inflated above the artery. The cuff is deflated and the pressure at which the pulse returns is recorded.
In a normal subject the pressure at the ankle pulses is slightly higher than at the elbow (there is reflection of the pulse pressure from the vascular bed of the feet, whereas at the elbow the artery continues on some distance to the wrist). The ABPI is the ratio of the ankle to arm pressure and an ABPI of greater than 0.9 is considered normal, suggesting that there is no significant peripheral vascular disease affecting the vessels of the legs. A reduced ABPI (less than 0.9) is consistent with peripheral artery occlusive disease (PAOD), with values below 0.8 indicating moderate diseased and below 0.5 severe disease.
However, a value greater than 1.3 is considered abnormal, and suggests calcification of the walls of the arteries and noncompressible vessels, reflecting severe peripheral vascular disease.
Studies in 2006 suggests that an abnormal ABPI may be an independent predictor of mortality, as it reflects the burden of atherosclerosis. [1] [2]
- Ankle and brachial systolic pressures taken using a hand-held Doppler instrument
- Supine, after ~10 minutes rest
- The resting ABI should be used to stablish the lower extremity PAD diagnosis in patients with suspected lower extremity PAD
- Exertional leg symptoms
- Non healing wounds
- 70 years and older or 50 years and older with history of smoking or diabetes
- ABI should be measured in both legs in all new patients with PAD of any severity to confirm the diagnosis and establish a baseline
- The toe-brachial index should be used to establish the lower extremity PAD diagnosis in patients in whom lower extremity PAD is clinically suspected but in whom the ABI test is not reliable due to noncompressible vessels (advance age or diabetes)
- Leg segmental pressure measurements are useful to establish the lower extremity PAD diagnosis when anatomic localization of lower extremity PAD is required to create a therapeutic plan.
References
- ↑ Feringa HH, Bax JJ, van Waning VH, Boersma E, Elhendy A, Schouten O, Tangelder MJ, van Sambeek MH, van den Meiracker AH, Poldermans D (2006). "The long-term prognostic value of the resting and postexercise ankle-brachial index". Arch Intern Med. 166: 529–535. PMID 16534039.
- ↑ Wild SH, Byrne CD, Smith FB, Lee AJ, Fowkes FG (2006). "Low ankle-brachial pressure index predicts increased risk of cardiovascular disease independent of the metabolic syndrome and conventional cardiovascular risk factors in the Edinburgh Artery Study". Diabetes Care. 29 (3): 637–42. PMID 16505519.