Risk factors and haemodynamic variables in patients with low toe-brachial index but normal ankle-brachial index

Classically, peripheral arterial disease (PAD) is diagnosed by a low ankle-brachial index (ABI), but the diagnosis can also be made based on toe-brachial index (TBI) measurements. The objective of this study was to characterize patients with low TBI but normal ABI, and chart potential underestimation of PAD prevalence by solitary use of ABI.

A total of 3739 consecutive patients with known or suspected PAD referred for ABI and TBI measurements in a four-year period were compared to an age- and gender matched control group (n = 17,340).

In the patient cohort, 65.0% had low ABI, 20.5% had low TBI but normal ABI, and 14.5% had normal indices. When comparing the frequencies of comorbidities related to atherosclerotic disease (myocardial infarction, congestive heart failure, cerebrovascular disease, diabetes mellitus, chronic kidney failure), there were no significant differences among patients with low ABI or low TBI with normal ABI in any of the variables (all p > 0.06). Of the patients with low TBI and normal ABI, 18.7% were diagnosed with diabetes mellitus type I or II, and 8.2% with chronic kidney disease.

Patients with low TBI but normal ABI represented 20.5% of patients referred with the suspicion of PAD. Furthermore, patients with low TBI but normal ABI presented similar comorbid characteristics to patients with low ABI, who have a well-described increased risk of cardiovascular morbidity and mortality. The solitary use of ABI underestimated the prevalence of PAD in the population, and PAD screening could potentially be improved by routine application of TBI.