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Variability of ankle-arm index in general population according to its mode of calculation
Background:
Ankle-arm index (AAI) is commonly used in epidemiological studies on peripheral arterial disease but its mode of calculation varies throughout the literature. We aimed to study the variance of the different measurements required to calculate the AAI according to different formulas, in order to find out the best way of AAI calculation, based on its lesser variability.
Methods:
A sample of 222 subjects from the general population was prospectively studied. Ten persons were excluded because of the presence of intermittent claudication or due to a lack of a Doppler posterior tibial artery (PT) signal. The systolic pressures of both arms, the dorsalis pedis arteries (DP) and the PT were finally measured in 212 healthy persons (mean age 49.9, range 18-101).
Results:
Methods using the lowest ankle artery pressure were excluded, as an absent pedal pulse may not be abnormal. The mode using the lowest variance was the choice of the highest pressure between PT and DP of each leg divided by the mean of the systolic pressures of both arms.
Conclusions:
We recommend this mode of AAI calculation in epidemiological studies. As the variances of the measurements used are the lowest, it would be easier thereafter to determine normal ranges and cutoff points.