ABI derived from the highest and lowest ankle pressure. What is the difference?

Different modes of ankle-brachial -index (ABI) calculation lead to different information. We looked for the peripheral arterial disease (PAD) prevalence estimated from ABI-high and ABI-low and analysed the effect of age and classical risk factors.

Based on the Arteriomobil Project data, ABI was calculated considering the lowest of the four ankle artery pressures (ABI-low) or the higher ankle artery pressure of each leg (ABI-high), respectively. ABI <0.9 were defined to prove PAD.

Prevalence of PAD estimated using ABI-low was much higher than those using ABI- high (15.7% vs. 8.0%). Thus 8% of men and 7.5% of women suspected for PAD were not detected if prevalence rates are based on ABI-high alone. Estimating PAD prevalence only by measuring posterior tibial artery (ATP) pressure, prevalence rates were lowest with 2.4% for the left and 2.7% for the right ATP. Estimating PAD prevalence only by measuring anterior tibial artery pressure, prevalence rates were slightly higher, but still low. ABI-high systematically shows lower prevalence rates compared to ABI-low without divergence of the prevalence rates with increasing age. This parallelism of the curves remained unchanged when prevalence rates were separated for self-reported risk-factors; smoking, hypertension, hypercholesterolemia and diabetes.

The presented analysis of the Arteriomobil Project data support the hypothesis that the differences in prevalence rates estimated from ABI-high and ABI-low are mainly determined by anatomic variations of the plantar arch. Additional angiographic controlled studies are necessary to prove this hypothesis.