Diagnostic tools to establish the presence and severity of peripheral arterial disease in people with diabetes: a synopsis of the DM PAD prospective multicentre diagnostic accuracy study.

Abstract

Background: Peripheral arterial disease is a major cause of the development of diabetic foot ulcers, lower limb amputation and mortality in patients with diabetes. Diagnosing peripheral arterial disease is of clinical importance but is difficult in this cohort of patients. Several diagnostic bedside tests exist, but there is uncertainty as to which is the most accurate.

Objective(s): To determine the diagnostic accuracy of five index tests (audible waveform assessment, visual waveform assessment, toe-brachial pressure index, ankle-brachial pressure index and exercise ankle-brachial pressure index) for the diagnosis of peripheral arterial disease in patients with diabetes as determined by a reference test (computed tomography angiography or magnetic resonance angiography). In selected sites, to evaluate the performance of a sixth test, the Podiatry Ankle Duplex scan, a new point-of-care duplex ultrasound scan.

Design and methods: Prospective multicentre diagnostic accuracy study.

Setting: Primary (general practice and community clinics) and secondary care National Health Service hospitals (inpatient and outpatient) in the United Kingdom.

Participants: Patients were eligible for inclusion if they were aged ≥ 18 years and had a known history of diabetes. Exclusion criteria included contraindications to computed tomography angiography or magnetic resonance angiography, if their peripheral arterial disease status was known on imaging, or they had a known history of peripheral arterial disease intervention.

Interventions: Participants underwent all bedside tests (Podiatry Ankle Duplex scan performed in three centres only), which were performed in a logical sequence to reduce the risk of bias. The reference scan was to be performed within 6 weeks of the index tests.

Main outcome measures: The primary outcome measure of diagnostic performance is test sensitivity. Secondary outcomes included specificity, likelihood ratios, predictive values and diagnostic odds ratio, as well as patient acceptability of tests, technical success and health economic outcomes.

Results: Based on the 573 reference tests performed, 222 (39%) participants had evidence of peripheral arterial disease. All routinely used index tests showed relatively low sensitivities: audible waveform 36%, 99% confidence interval 27% to 45%; visual waveform 42%, confidence interval 33% to 51%; toe-brachial pressure index 55%, confidence interval 46% to 64%; ankle-brachial pressure index 41%, confidence interval 32% to 50%; and exercise ankle-brachial pressure index 41%, confidence interval 31% to 51%. The Podiatry Ankle Duplex scan had a higher sensitivity 89%, confidence interval 74% to 100%, as compared to all other index tests.

Limitations: A large proportion of reference scans were performed outside the 6-week time window (45%), although peripheral arterial disease is a chronic condition and is unlikely to have developed/progressed in the time frame. Additionally, the peripheral arterial disease prevalence was lower than anticipated during study design (39% vs. 50%). Lastly, despite efforts to standardise assessment and minimise bias, there is the possibility that one test may have influenced the interpretation of others.

Conclusions: Index tests used routinely in clinical practice for diagnosing peripheral arterial disease in patients with diabetes showed poor diagnostic accuracy for peripheral arterial disease and should not be recommended for diagnosing peripheral arterial disease in this population.

Future work: A review of peripheral arterial disease diagnostic testing in patients with diabetes should be undertaken. It may be necessary to perform more reliable imaging, such as full lower limb duplex ultrasound as a first-line diagnostic test.

Funding: This synopsis presents independent research funded by the National Institute for Health and Care Research (NIHR) Health Technology Assessment programme as award number NIHR131855.