The predictive value of vascular calcification on plain radiographs of the ankle to diagnose diabetes mellitus

Introduction: There are nearly 500,000 people with undiagnosed diabetes mellitus in the UK. A common complication of diabetes is vascular calcification. The incidental finding of vascular calcification on plain radiographs in patients with undiagnosed diabetes has the potential to alter patient management. We hypothesised that the presence of vascular calcification on plain radiographs of the foot may predict the diagnosis of diabetes and aimed to determine the positive predictive value of vascular calcification to diagnose diabetes.

Methods: A retrospective case control study compared 130 diabetic patients to 130 non-diabetic patients that were matched for age and gender. The presence of vascular calcification in anterior, posterior or plantar vessels was measured on plain radiographs. McNemar's Chi-squared test and positive predictive values were calculated. Conditional logistic regression models estimated the association between calcification and diabetes RESULTS: The overall mean age was 58.0 % and 31.5 % were females. 89.2 % of those with diabetes had calcification present, and 23.1 % in those who did not have diabetes had calcification. McNemar's test for independence gives p < 0.001. Calcification in both anterior and posterior vessels predicts diabetes with a positive predictive value of 91.2 % (95 % CI 76.9-97.0 %). The odds ratio for having diabetes is 78 (95 % CI: 7.8 - 784) times higher in a person who has calcification in the blood vessels of their ankle than in a person without calcification after adjusting for confounders CONCLUSION: This study has demonstrated that vascular calcification in the anterior and posterior blood vessels is over 90 % predictive of a diagnosis of diabetes. This screening test could be used in future clinics when interpreting radiographs, aiding in the diagnosis of diabetes and altering patient management.