title: Test characteristics of the ankle-brachial index and ankle-brachial difference for medial arterial calcification on X-ray in type 1 diabetes.
abstract: OBJECTIVE
  Medial arterial calcification (MAC) is common in diabetes, has a characteristic appearance on X-ray imaging, and has been linked with peripheral arterial stiffness and cardiovascular disease. However, few studies have measured X-ray MAC. It has been suggested that an ankle-brachial index (ABI) >1.30 or an ankle-brachial difference (ABD) >75 mm Hg may identify X-ray MAC, but test characteristics are unknown. We hypothesized that an ABI >1.30 and ABD >75 mm Hg would have high specificity but low sensitivity for MAC on X-ray imaging.
  
  
  METHODS
  This was a cross-sectional study of 185 community-living individuals with type 1 diabetes. The ABI and the ABD were assessed. The outcome was linear "tram-track" calcifications in the lower limbs characteristic of MAC.
  
  
  RESULTS
  Mean age was 32 ± 6 years, and mean diabetes duration was 23 ± 7 years. X-ray MAC was noted in 97 individuals (57%), 15 (8%) had ABI >1.30, and 14 (8%) had ABD >75 mm Hg. As assessed by the ABI, the area under the receiver operating characteristic curve for MAC was modest (0.65) and was slightly higher for the ABD (0.75). An ABI >1.30 had high specificity (99%) and positive predictive value (93%) but poor sensitivity (14%) and an overall accuracy of 55% for MAC. An ABD >50 mm Hg remained highly specific (98%) but had higher sensitivity (30%) and overall accuracy (62%).
  
  
  CONCLUSIONS
  Individuals with type 1 diabetes and an ABI >1.30 or ABD >50 mm Hg are very likely to have MAC on X-ray imaging, yet many with MAC will not have an ABI or ABD above these thresholds. Given the high specificity, evaluating high ABI or ABD may be useful to understand correlates of MAC but may underestimate MAC prevalence.
authors.affiliation: Nephrology Section, Veterans Affairs San Diego Healthcare System, University of California, San Diego, San Diego, Calif 92161, USA. joeix@ucsd.edu
authors.forename: Joachim H
authors.initials: JH
authors.lastname: Ix
authors.forename: Rachel G
authors.initials: RG
authors.lastname: Miller
authors.forename: Michael H
authors.initials: MH
authors.lastname: Criqui
authors.forename: Trevor J
authors.initials: TJ
authors.lastname: Orchard
mesh_terms: D000328:Adult; D000704:Analysis of Variance; D055109:Ankle Brachial Index; D016009:Chi-Square Distribution; D003430:Cross-Sectional Studies; D003922:Diabetes Mellitus, Type 1 / Q000175:diagnosis* / Q000453:epidemiology / Q000503:physiopathology; D003925:Diabetic Angiopathies / Q000175:diagnosis* / Q000000981:diagnostic imaging / Q000453:epidemiology / Q000503:physiopathology; D005260:Female; D006801:Humans; D035002:Lower Extremity / Q000098:blood supply*; D008297:Male; D008875:Middle Aged; D010414:Pennsylvania / Q000453:epidemiology; D011237:Predictive Value of Tests; D011446:Prospective Studies; D012372:ROC Curve; D011859:Radiography; D018570:Risk Assessment; D012307:Risk Factors; D012680:Sensitivity and Specificity; D012720:Severity of Illness Index; D016909:Tibial Arteries / Q000000981:diagnostic imaging* / Q000503:physiopathology*; D061205:Vascular Calcification / Q000175:diagnosis* / Q000000981:diagnostic imaging / Q000453:epidemiology / Q000503:physiopathology; D055815:Young Adult