Ankle brachial pressure index

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.