The current study showed that number and severity of diabetes complications both are independently associated with increased risk of mortality and hospitalization in a population-based sample of primary care patients with diabetes. When directly compared, the DCSI performed slightly better than a simple count of diabetes complications to predict mortality and hospitalizations, although both the DCSI and the count of complications performed well.
Prior studies of patients with diabetes have used retrospective cohort analyses to develop prediction rules for incident cardiovascular disease (eg, the Framingham Heart Study31
and the United Kingdom Prospective Diabetes Study12
risk engines), for short-term complications,13
for risk management or prediction,14
and for cost analysis.27
However, to our knowledge, no severity index based on laboratory and automated data has been developed and tested to predict mortality and hospitalizations in patients with diabetes. The DCSI differs from other risk engines in that it is an index to better identify severity and gives researchers or health plan administrators an easy, reliable method to risk-adjust for severity of diabetes when self-reported variables or additional laboratory variables are not available. Given that healthcare plans have limited resources to improve disease management for diabetes, this index should allow healthcare plans to target these resources to the highest risk group of patients.
As several prior epidemiologic studies have shown, diabetes substantially increases the risk of all-cause and cardiovascular mortality for both men and women by 2- to 4-fold.15,16,19,32,33
Miettinen and colleagues showed that diabetes increased mortality significantly after the first myocardial infarction.34
In the current study, we found that the DCSI (capturing the type and severity of complications) versus a simple count of complications was more strongly associated with mortality and hospitalization.
The current study expands the existing literature by evaluating concurrent risk of mortality associated with cardiovascular disease, nephropathy, retinopathy, peripheral vascular disease, and neuropathy as indicators of diabetes severity. Several studies have shown that other individual complications such as underlying severe diabetic retinopathy,35,36
early and severe diabetic nephropathy, peripheral vascular disease, hyperglycemia, and metabolic abnormalities increase the risk of mortality. In both younger and older diabetic subjects, proliferative diabetic retinopathy compared with no diabetic retinopathy was associated with an increased risk of cardiovascular disease35
In addition, early (microalbuminuria) and overt diabetic nephropathy have been shown to be risk factors for cardiovascular disease and mortality.39
Patients with later stages of chronic kidney disease and advanced diabetic nephropathy have a greater risk of complications and mortality than patients without renal disease.40
In addition, data from the Coronary Artery Surgery Study registry showed that patients with lower extremity arterial disease had a 1.2-fold greater risk of death than patients without baseline lower extremity arterial disease.41
The current study augments these data by providing an estimation of risk of death and hospitalization in relation to the number and severity of complications, which is useful in actual clinical settings, where more than 1 complication often is present.
Duration of diabetes also has been determined to be an independent risk factor for an increased risk of cardiovascular events18
and for development of certain complications such as microalbuminuria.42
We found that duration was independent of and highly correlated with both the individual count of complications and the severity index. Duration became a less significant predictor of mortality after the addition of either complications count or the severity index to the Cox models. The development of diabetes complications may serve as a surrogate marker for diabetes duration. Because the diagnosis of type 2 diabetes often is not made until years after its onset, the number and severity of complications may better represent biologic markers of duration of diabetes after adjustment for other potential confounding variables.43
This study has several potential limitations. The data obtained at baseline were observational, and as such, not all laboratory data were collected on all patients at entry into the study. However, all prior events were collected by the automated databases and because the categorization of severity was most dependent on prior hospitalizations, this limitation should be minimal. In addition, because the study was based on clinical practice at the time of data ascertainment at a single healthcare system in 1 geographic region of the United States, it may not be representative of populations in other regions of the United States. The study population, however, has been shown to be representative of Washington State population, with the exception of lower representation in the highest income status. A final limitation is that the DCSI is an unweighted index that did not independently test adverse outcomes associated with each complication; however, the advantage of the DCSI is its ease of use by clinicians, researchers, and healthcare plans.