Diabetes and Prior Coronary Heart Disease are Not Necessarily Risk Equivalent for Future Coronary Heart Disease Events

For more than a decade, the presence of diabetes has been considered a coronary heart disease (CHD) "risk equivalent". The objective of this study was to revisit the concept of risk equivalence by comparing the risk of subsequent CHD events among individuals with or without history of diabetes or CHD in a large contemporary real-world cohort over a period of 10 years (2002 to 2011). Population-based prospective cohort analysis. We studied a cohort of 1,586,061 adult members (ages 30-90 years) of Kaiser Permanente Northern California, an integrated health care delivery system. We calculated hazard ratios (HRs) from Cox proportional hazard models for CHD among four fixed cohorts, defined by prevalent (baseline) risk group: no history of diabetes or CHD (None), prior CHD alone (CHD), diabetes alone (DM), and diabetes and prior CHD (DM + CHD). We observed 80,012 new CHD events over the follow-up period (similar to 10,980,800 person-years). After multivariable adjustment, the HRs (reference: None) for new CHD events were as follows: CHD alone, 2.8 (95 % CI, 2.7-2.85); DM alone 1.7 (95 % CI, 1.66-1.74); DM + CHD, 3.9 (95 % CI, 3.8-4.0). Individuals with diabetes alone had significantly lower risk of CHD across all age and sex strata compared to those with CHD alone (12.2 versus 22.5 per 1000 person-years). The risk of future CHD for patients with a history of either DM or CHD was similar only among those with diabetes of long duration (a parts per thousand yen10 years). Not all individuals with diabetes should be unconditionally assumed to be a risk equivalent of those with prior CHD.