I have followed the electron-beam computed tomography coronary calcium-screening phenomenon with great interest. Although there were other precedents, it was my introduction to the mass marketing of a diagnostic test to the public. Having been trained as a nuclear cardiologist in the era of Diamond and Forrester’s landmark article, “Analysis of probability as an aid in the clinical diagnosis of coronary artery disease,”1
I could not imagine how a test with less-than-perfect sensitivity and specificity could provide useful diagnostic information without regard
to the patient’s pretest likelihood of having coronary artery disease (CAD), or even more importantly, their likelihood of having a coronary event. It is now years later; tens of thousands of individuals (it’s not clear how many are actually patients) have been tested, and yet the clinical value of electron-beam computed tomography coronary calcium scoring remains to be established.The article by Sevrukov and colleagues (page 30) describes an analysis of 30,904 asymptomatic individuals who were self-referred for electron-beam computed tomography between 1993 and 1999. Diabetes was reported by 3.4% of the men and 3.8% of the women. Average calcium scores were higher for patients with diabetes than for those without. One notable exception was for patients over age 70, who had similarly high calcium scores independent of self-reported diabetes.
The authors state that it is unknown whether electron-beam computed tomography screening adds important information to traditional CAD risk factors in asymptomatic diabetic individuals. Why the test was performed on these subjects if the answer to this question was not known is a topic for another discussion. Since the submission of this manuscript, more information has become available. A study from the South Bay Heart Watch suggests that electron-beam computed tomography does not add important information.3 A total of 1,312 diabetic and nondiabetic subjects underwent risk factor screening and electron-beam computed tomography and were followed up clinically for 6.3 ± 1.4 years. Although subjects with diabetes were more likely than nondiabetic subjects to have coronary events, Cox regression analysis revealed that coronary calcium score risk groups were significantly associated with events only in nondiabetic subjects, but not in diabetic subjects.
The probability of a future coronary event among diabetic individuals is roughly equivalent to that of survivors of a myocardial infarction, which is a strong rationale for current recommendations for aggressive secondary prevention schemes for diabetic patients.4,5 This strategy should not be influenced by coronary calcium scores. Sevrukov and colleagues call for clinical research to address the potential uses of coronary artery calcium screening in individuals with diabetes or those at risk of developing diabetes. Unfortunately, a strong case has not been advanced to support such a project, and at present, there is no clear clinical justification for electron-beam computed tomography calcium screening among patients with diabetes.