Peripheral arterial disease (PAD) is common below the knee in diabetes but arteries in the foot are controversially said to be spared of occlusive disease. This is relevant to the convenient site of vascular assessment that is recommended in guidelines. Should assessment be distal at toe/forefoot to detect foot disease or only proximal to detect disease at ankle level? The objective was to determine frequency of PAD at foot and ankle level. This was a cross-sectional observational study, evaluating arterial disease proximally by palpation of pedal pulses and Ankle Brachial Index (ABI), and distally by Toe Brachial Index (TBI), and forefoot transcutaneous oxygen tension (tcpO2), in consecutive patients presenting with foot ulceration. We assessed 301 limbs in 154 patients: 59% of limbs were ulcerated. PAD in the foot was detected in 70% and 74% of limbs by TBI and forefoot tcpO2, respectively, but PAD at ankle level only in 51% and 34% by pulse palpation and ABI, respectively. In limbs with "normal" ABI, PAD was present in the foot in 70% as indicated by low TBI, and in 73% by low tcpO2, with 70% to 64% having associated ulceration, respectively. When compared with arterial waveforms, as a measure of PAD, TBI gave an excellent AUC (area under the curve of the receiver operating characteristic curve) of 0.81 (95% confidence interval: 0.73-0.89), but ABI gave a poor AUC of 0.65 (95% confidence interval: 0.55-0.76). In conclusion, arterial disease is important in the foot and can be detected by TBI, which should be performed even when ABI is normal. Guidelines that recommend TBI only if ABI is artificially raised need updating.
Keywords: ABI; Ankle Brachial Index; TBI; Toe Brachial Index; foot ulceration; peripheral arterial disease.