In this study of patients receiving care in two integrated delivery systems, we found that 16% and 30% of individuals with diabetes, hypertension and hyperlipidemia achieved simultaneous control of all three conditions, as defined by 2002 ADA guidelines,17
over a median of 4.0 and 4.4 years of follow-up. Among those with at least 90 days of follow-up after achieving simultaneous control, only 13% and 5% of the DH and KP cohorts, respectively, maintained simultaneous control until the end of the observation period. The predictors of ever achieving simultaneous control were similar in the two populations. Socio-demographic and clinical characteristics did not discriminate accurately between individuals who attained simultaneous control and those who did not, while maximum risk factor values, medication patterns, and medication adherence improved model discrimination.
Prior studies of simultaneous risk factor control among individuals with diabetes have reported prevalence rates, while we determined incidence rates. Incidence data has the advantage of giving a fuller picture of what a cohort of individuals is able to achieve over time, as well as allowing examination of maintenance of control. Previously reported prevalence rates from several countries have been low, mostly in the 5-20% range.3-11
For example, a study using NHANES data found the prevalence of simultaneous achievement of a HbA1c
< 7.0%, blood pressure < 130/80 mmHg, and LDL cholesterol < 100 mg/dL was 7.0% in 1999-2002 and 12.2% in 2003-2006.3
A study from the VA National Diabetes Registry in 1999-2000, using the same criteria, found a 3.9% rate of simultaneous control.11
Most previous studies have only examined one set of criteria for achievement of simultaneous control. The study from the VA National Diabetes Registry also examined less stringent criteria (HbA1c
< 9%, blood pressure < 140/90 mmHg, and LDL cholesterol < 130 mg/dL) and found a prevalence of 30.7%.11
In the last several years, the optimal level of risk factor control to prevent macrovascular outcomes has been a matter of increasing debate.23, 24
In addition, there has been an ongoing discussion about whether item-by-item measurements, composite measurements, or all-or-none measurements are the most effective for judging quality of care and motivating improvement in quality.25, 26
All-or-none measurements, such as our assessment of simultaneous risk factor control in diabetes, takes the patient's perspective, as the patient is the unit of analysis.25
It is also a more sensitive measure of quality improvement than item-by-item measurements.25
Our study illustrates that when continuous measurements (such as HbA1c
, blood pressure, and LDL cholesterol) are transformed into dichotomous threshold-based measures, relatively small differences in cut-points can have large effects on conclusions concerning quality of care. Selection of an appropriate threshold can be difficult, especially with the greater emphasis on individualized clinical goals in diabetes.26, 27
Using high threshold goals ensures that the goals are appropriate for almost all individuals and focuses attention on individuals that are the furthest from the optimal levels and who therefore have the most to gain. However, it does not encourage the health care system to help most individuals achieve optimal levels. In contrast, using stricter threshold goals means the risks of the resulting aggressive treatment will exceed the potential benefits for some individuals.26
The frequency of risk factor measurement has implications for our assessment of simultaneous control. Individuals could only be in simultaneous control if they had all three risk factors measured within 90 days. The differences in the risk factor measurement rates between those who did and did not achieve simultaneous control were relatively small. Increasing the allowed period for achieving simultaneous control did not substantially change our findings. The frequency of risk factor measurement also has implications for the maintenance of simultaneous control, since individuals could only fall out of simultaneous control when they had risk factors measured. The specific timing of risk factor measurements is the result of a number of complex factors, including the risk factor levels themselves, patients' level of engagement with the healthcare system, and both clinicians' and patients' perception of underlying risk. Most people lost simultaneous control because of elevated blood pressure, which likely reflects both the greater frequency of blood pressure measurements and the greater intraperson variability of blood pressure.
Prior studies found that males,7, 11, 28
whites,6, 11, 28
older individuals,7, 28
those with greater education28
and individuals with cardiovascular disease and lower body mass index6, 7, 11, 28
were more likely to achieve simultaneous control. Prior studies also found that achieving simultaneous control is associated with receiving cholesterol-lowering medications and fewer antihypertensive medications, and not receiving insulin.6, 11, 28
These findings are largely consistent with ours.
The higher rate of simultaneous control in KP compared to DH is likely the result of both patient level and system level factors. Compared to the KP population, the DH population has a much higher proportion of individuals with low socioeconomic position; the reasons for poorer health in socioeconomically disadvantaged individuals are complex but likely result from more than just limited access to healthcare.29
Second, based on our multivariable models, the KP cohort would be predicted to have a higher rate of simultaneous control based on its age, gender, disease severity, and comorbidity profile. Third, the higher medication adherence of the KP cohort than the DH cohort likely explains some of the differences. Fourth, differences in physician practices between the two systems, such as different degrees of treatment intensification or different goal setting, could potentially explain some of the differences. Finally, KP has been able to devote substantially more resources to population based management systems over a period of many years. Population-based mechanisms for identifying individuals who have not achieved simultaneous control and treating elevated risk factors could potentially help improve achievement and maintenance of simultaneous control. Focusing on blood pressure, in particular, would be most likely to increase achievement of simultaneous control.
Our findings contribute to the literature in several ways. First, we assessed achievement of simultaneous control in two disparate health care systems within the same region. Second, our longitudinal study could assess incidence rather than simply prevalence of simultaneous control. As a result, we determined that sustained simultaneous risk factor control was rare and brief, especially using stringent guidelines. Third, no prior study has assessed either the severity of the individual diseases, medication adherence, or health care utilization as correlates of simultaneous control. Finally, although prior studies had identified socio-demographic and clinical variables associated with simultaneous control, they did not report the discrimination of their statistical models. The low c-statistics of Model 1 suggests that clinicians and researchers need to look beyond these conventional and easily obtainable measures if they are to identify useful predictors of self-management for diabetes.30
This study has several limitations. First, because we took advantage of existing cohorts, the inclusion and exclusion criteria differed slightly for the two different health care systems. Second, since all data were obtained in routine clinical practice, the number of measurements of clinical and timing of outcomes was variable, and there was missing data on some variables (most notably medication use in DH and race information in KP). Third, we were not able to determine the pre-treatment severity of diabetes, hypertension or hyperlipidemia, and had to use the highest available measurement, which could be confounded by a number of factors, as a proxy. Fourth, individuals could receive services from other health care providers and systems, although this was likely limited. For all these reasons, our findings may not be generalizable to other populations or settings.
Individuals who are able to achieve simultaneous treatment goals can be viewed as “positive deviants,”31, 32
whose strategies for self-care may provide important lessons for other individuals. The degree of statistical discrimination provided by a multivariable model based only on socio-demographic factors and clinical diagnoses suggests that assessment of self-care behaviors may be necessary to explain the ability of these individuals to attain control of their conditions. Although our ability to measure such behavioral characteristics was limited, medication adherence emerged as a strong predictor of simultaneous control, while tobacco use and substance abuse were unrelated to treatment outcomes. Assessment of the behavioral strategies that these individuals use to facilitate their adherence with medications or other elements of self-care will require additional quantitative and qualitative research.
In summary, we found that in two large cohorts 16-30% of individuals were able to achieve simultaneous, but generally transient, control of diabetes, hypertension, and hyperlipidemia over a median of 4.0-4.4 years of follow-up. Small changes in the treatment goals had a relatively large effect on the proportion considered to be at goal. Efforts to understand the strategies that such individuals, particularly those with durable control, use to balance the demands of their multiple health conditions may help define interventions to improve self-care and health outcomes among the increasing population of individuals with multiple, chronic health conditions.