Noninvasive Arterial Testing in Patients with Diabetes

Background: This study was designed to compare the findings of noninvasive arterial testing in patients with and without diabetic foot pathology. Methods: The ABI (ankle brachial index), TBI (toe brachial index), and great toe pressures were measured in 207 patients. PAD (peripheral artery disease) was defined as an ABI < 0.91 on either extremity or a TBI < 0.7. Results: PAD was identified in 103 of the 207 patients (49.8%), 80 patients with diabetic foot pathology and 23 patients with nondiabetic foot pathology. Although patients with diabetic foot pathology were 1.4 times more likely to have PAD compared to patients without diabetic pathology, this increased risk was not statistically significant (OR 1.41 [95% CI 0.75-2.64], P =.28). Patients with PAD and diabetic foot pathology were 4.9 times more likely to have ischemia (toe pressure < 60 mm Hg) than patients with PAD and nondiabetic foot pathology (OR 4.93 [95% CI 1.35-17.94], P <.05). Patients on dialysis had a 7.3 times increased likelihood of having PAD compared to patients not on dialysis (OR 7.3 [95% CI 1.6-33.6], P <.01). Patients with absent pedal pulses were 4.9 more likely to have PAD than patients with normal pulses (OR 4.9 [95% CI 2.6-9.4], P <.0001). PAD was identified in 97 of 188 patients (51.6%) with peripheral neuropathy compared to 6 of 19 patients (31.5%) without peripheral neuropathy (OR 2.31 [95% CI 0.84-6.33], P =.10). Conclusions: Combining the ABI with TBI improved the ability to diagnose PAD in diabetic patients because the ABI has high specificity (low false positives) and the TBI has high sensitivity (low false negatives). The TBI was more reliable in patients with noncompressible arteries, medial artery calcinosis and/or neuropathy. Due to the relative incompressibility of calcified distal arteries in patients with DM, the ABI may be within normal limits in patients with PAD. This false negative result may lead surgeons to assume that normal perfusion is present. Level of Evidence: Level III, comparative study.