Absence of coronary artery calcium identifies asymptomatic diabetic individuals at low near-term but not long-term risk of mortality: A 15-year follow-up study of 9715 patients

Background - Data regarding coronary artery calcification (CAC) prognosis in diabetic individuals are limited to 5-years follow-up. We investigated the long-term risk stratification of CAC among diabetic compared with nondiabetic individuals. Methods and Results - Nine thousand seven hundred and fifteen asymptomatic individuals undergoing CAC scoring were followed for a median (interquartile range) of 14.7 (13.9-15.6) years. The incidence density rate and hazard ratios with 95% confidence intervals were used to calculate all-cause mortality. Incremental prognostic utility of CAC was evaluated using the area under the receiver operator characteristic curve and net reclassification improvement. Diabetics (54.7±10.8 years; 59.4% male) comprised 8.3% of the cohort (n=810), of which 188 (23.2%) died. For CAC=0, the rate of mortality was similar between diabetic and nondiabetic individuals for the first 5 years (P>0.05), with a nonlinear increased risk of mortality for diabetics after 5 years (P<0.05). The adjusted risk of death for those in the highest (CAC>400) versus the lowest (CAC=0) category of CAC increased by a hazards of 4.64 (95% confidence interval =3.74-5.76) and 3.41 (95% confidence interval =2.22-5.22) for nondiabetic and diabetic individuals, respectively. The presence of CAC improved discrimination (area under the receiver operator characteristic curve range: 0.73-0.74; P<0.01) and reclassification (category-free net reclassification improvement range: 0.53-0.50; P<0.001) beyond conventional risk factors in nondiabetic and diabetic individuals, respectively. Conclusions - CAC=0 is associated with a favorable 5-year prognosis for asymptomatic diabetic and nondiabetic individuals. After 5 years, the risk of mortality increases significantly for diabetic individuals even in the presence of a baseline CAC=0.