Assessment of toe brachial index validity in diabetic patients - interim results

The toe brachial index (TBI) is recommended for the detection of lower extremity arterial disease (LEAD) in case of reduced efficacy of the ankle brachial index (ABI), which most often occurs in diabetics. In this case, TBI is expected to give more accurate results. There are not many studies dealing with the use of TBI specifically in diabetics and the results are different.

The purpose of this work is to present the interim results of the study, whose main objective is to assess the validity of TBI in diabetics and to determine whether this method provides improvements over the ABI.

In the first phase of the study, 42 limbs were examined in 21 patients with type 2 diabetes. ABI was measured using the automatic oscillometric method (ABI OSC) and the manual method using the pencil doppler (ABI DPP). TBI was determined using an automatic plethysmographic method. The reference examination of the arteries of the lower limbs was performed using duplex ultrasonography (DUS). A paired t-test was used to compare the individual TBI and ABI methods. Cut-off points ABI < 0.9; TBI < 0.7; and DUS stenosis > 50 % were used to evaluate validity parameters.

The individual ABI and TBI methods gave different results (p < 0.05). In eight limbs of the total number, LEAD was demonstrated using DUS. The best validity parameters were demonstrated by the TBI - sensitivity 0.88; specificity 0.88; positive predictive value 0.64; negative predictive value 0.97, positive likelihood ratio 7.44; negative likelihood ratio 0.14. The ABI method of calculation, that uses lower systolic blood pressure determined from two measurement sites on the ankle as a numerator, had a higher validity parameters. The ABI OSC did not correctly detect a single limb with stenosis > 50 % in this cohort.

According to the interim results of this work, the TBI was more suitable for the detection of LEAD in diabetics in comparison with ABI.