A diagnostic dilemma: An investigation of non-invasive vascular assessment of the lower extremity in people with diabetes
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Authors: Chuter,V. H.;Craike,P. E.;Johnson,N. A.;Casey,S. L.
Start Page: S524
Background and aims: Peripheral arterial disease (PAD) is estimated to affect 21% of people over the age of 65. Non-invasive vascular assessment of the lower extremity using the ankle brachial index (ABI) is recommended to screen for the disease in those at risk of PAD including older people and people with diabetes. It is well known that the ABI loses clinical utility in the presence of diabetes and in older age due to the presence of medial arterial calcification (MAC). The toe-brachial index (TBI) is recommended as an alternative to the ABI where elevated ABI values suggest incompressible arteries due to MAC. However there is some research to suggest the TBI may be more clinically effective in all people with diabetes due to the presence of co-existant PAD and MAC producing normal ABI values in the presence of significant arterial pathology. The aim of this study was to investigate the comparative diagnostic accuracy of the TBI and ABI for the presence of PAD in people with and without diabetes.
Materials and methods: Participants meeting current guidelines for lower extremity vascular screening including people with diabetes were recruited on a volunteer basis from two university podiatry teaching clinics. ABI and TBI measurements were performed on the right lower extremity of all participants. Participants subsequently underwent colour duplex Ultrasound from the abdominal aorta to the distal ankle on the right side. This was used as the reference standard to calculate sensitivity, specificity and diagnostic accuracy of both the TBI and ABI for the presence of PAD. ROC analysis was performed to determine the clinical efficacy for diagnosis of PAD of each test. Results: One hundred and sixty nine people were recruited to this study including 89 people with Type 2 diabetes and 100 males, with a mean age 73.57 years (SD 7.31 years). The ABI has the highest specificity for PAD in both people with and without diabetes (specificity 93%, 95%CI 0.82 to 0.98 and 95%, 95%CI 0.84 to 0.98 respectively). The TBI had greater sensitivity than the ABI in people with and without diabetes (sensitivity with diabetes TBI: 85%, 95%CI 0.72 to 0.92, ABI: 42%, 95%CI 0.30 to 0.57, sensitivity without diabetes TBI: 89%, 95%CI 0.75 to 0.96, ABI: 61%, 95%CI 0.45 to 0.75). Overall, and, in the presence of diabetes, diagnostic accuracy was higher for the TBI (TBI: 78% and 88% respectively, ABI: 68% and 79% respectively). ROC analysis indicated the TBI had greater clinical efficacy for the diagnosis of PAD in people with diabetes and in the entire study population (ROC area:0.82 p=.0001, and 0.81 p=0.0001) than the ABI (ROC area:0.59, p=0.09, and 0.67,p=0.0001).
Conclusion: Our results demonstrated that the ABI had greater specificity for the presence of PAD than the TBI in people with and without diabetes. However, overall the TBI demonstrated greater diagnostic accuracy and may be more clinically effective than the ABI for diagnosing PAD in people with diabetes and those meeting current guidelines for PAD screening, particularly if PAD is suspected. Further research needs to evaluate relationships between severity and location of PAD and the relative clinical utility of the TBI and ABI in people with diabetes.