Ankle-to-brachial ratio index (ABI) is a simple method recommended for screening and evaluating peripheral arterial occlusive disease (PAOD) severity in diabetic patients. However, it has been suggested that subclinical media artery calcification could falsely normalize ABI (1), and prevalence of effective arterial occlusive disease when arteries are not compressible is not clear (2). Therefore, defining clinically relevant peripheral arterial occlusion on an ABI threshold of <0.9 could lead to misclassifying many diabetic patients, especially in a population at high risk for PAOD and arterial calcification (age, kidney disease, and hypertension). We evaluated the accuracy of ABI in screening and evaluating PAOD in such a population.
Inpatients from a single diabetes department were consecutively included if they had any of the following conditions, which indicate high risk for PAOD: history of coronary heart disease, significant carotid stenosis, any palpable pulse abnormality in the foot, and/or presence of a foot ulcer. Patients with previous lower-limb revascularization procedure were excluded. ABI was measured in the dorsalis pedis artery or, if undetectable, in the posterior tibial artery, and the number and extent of anatomical arterial stenoses were determined by color-flow duplex ultrasound scan. An adapted version of an angiographic score was used to measure the severity of stenosis in the aortoiliac and femoropopliteal segments, the tibioperoneal trunk, and the anterior tibial, posterior tibial, and peroneal and dorsalis pedis arteries: 0, <70% stenosis; 2, >70%; and 3, occluded. The final score ranged from 0 to 21.
Eighty-three patients (162 lower limbs) were included (mean ± SD age 65 ± 12 years, 69% male, diabetes duration 21 ± 13 years, type 2 diabetes 83%, coronary heart disease 44%, glomerular filtration rate <60 ml/min 40%, foot ulcer 76%, neuropathy 77%, and hypertension 84%). ABI was between 0.9 and 1.3 in 67 (43%) lower limbs (group 1), <0.9 in 66 (42%) (group 2), and >1.3 in 24 (15%) (group 3). The color-flow duplex ultrasound scan highlighted the presence of PAOD in 57% of the lower limbs from group 1 (“falsely normal”), 85% from group 2, and 58% from group 3. When PAOD was present, the score of severity was higher in group 3 (8.4 ± 5) than in group 2 (7.4 ± 4.4) (P < 0.047).
Our results show that in a selected diabetic population at high risk for PAOD, the prevalence of effective PAOD among patients with an ABI between 0.9 and 1.3 and >1.3 is high (57 and 58%, respectively). This can be explained by the high risk for arterial calcification in such a population (3), leading to overestimating ankle arterial pressure. The high rate of peripheral neuropathy in these populations may also play a role given its known association with medial calcification (4,5). Altogether, these results suggest that ABI is not a reliable screening method for diagnosis of PAOD in high-risk diabetic patients because it may lead to missing or misclassifying significant occlusive lesions.
Acknowledgements
No potential conflicts of interest relevant to this article were reported.