We found a distinct association between discordant comorbidities and a composite endpoint of initiating lipid-lowering therapy or achieving a desirable LDL cholesterol level in this cohort of primary care patients with hypertension and elevated LDL cholesterol. Increasing numbers of discordant conditions decreased the adjusted odds of guideline-consistent hyperlipidemia management, a finding that persisted despite the presence of conditions that increase the risk of cardiovascular events or death. An increasing number of concordant conditions was associated with increased likelihood of guideline-consistent hyperlipidemia management regardless of the number of discordant conditions. These results are consistent with the hypothesis that the type of comorbidity may have different effects on guideline-consistent hyperlipidemia management and that competing demands may negatively affect the quality of cardiovascular risk management even in the patients for whom it is most indicated.
The theory that different types of comorbidities have varying impacts on cardiovascular risk reduction has been previously suggested, 17,18
but few studies have addressed the separate roles of concordant and discordant conditions.22
Most research on the impact of comorbidity on cardiovascular risk reduction has combined concordant and discordant comorbidities. Several studies concluded that comorbidity may improve quality of care; others found that comorbidity detracts from quality.10-16
A recent example, a study by Higashi et al.,10
found that the presence of multiple medical conditions was associated with improved quality of care across many diseases and many quality indicators. The comorbidity measure used, however, was a simple count of conditions that did not distinguish between concordant and discordant comorbidity. This study also combined many quality measures that may exhibit various relationships with comorbid conditions. By separating discordant and concordant conditions and examining a single target condition, we were able to uncover distinctive effects that may have been obscured or confounded in Higashi’s study.
Our findings are supported by several studies that have separately investigated concordant and discordant patient comorbidities. Some have reported the positive impact of separate concordant comorbidities on the management of cardiovascular risk factors,23,24
whereas others have found negative impacts of individual discordant comorbidities on management of these risk factors.25–27
We believe this is the first study to examine the concurrent, separate, and linear contributions of concordant and discordant comorbidities on management of a single cardiovascular risk factor.
An increased likelihood of guideline-consistent hyperlipidemia management for patients with more concordant conditions is expected because coronary artery disease or its risk equivalent is a strong motivator for lipid management. The finding that an increasing number of discordant conditions (which may reflect competing demands) was associated with failure to manage high LDL cholesterol is more alarming. To confirm the consistency of this relationship, we tested for an interaction between concordant and discordant conditions. When no significant interaction was observed, we stratified our analyses to separately examine patients with and without concordant conditions and found very similar results for both groups. Our robust findings seem to indicate that discordant conditions may indeed be a significant barrier to high quality care.
However, our comorbidity measure did not allow us to determine the severity of a given discordant condition or identify clinically dominant conditions. Therefore, we were not able to distinguish between patients receiving poor quality care and those for whom initiation of therapy was not indicated. Conditions that are clinically dominant eclipse the management of all other conditions because they occupy a preponderance of the physician or patient’s time or affect a patient’s life expectancy.17
Because the inability to determine severity of a given condition is a weakness of ICD-9-CM-based comorbidity measures, 28–36
future research should focus on methods to determine whether specific, severe comorbidities are driving the observed relationship between the number of discordant conditions and guideline-consistent care for LDL cholesterol management.
The outcome used in this study (i.e., guideline-consistent care) was not a performance measure because we did not designate a time frame for initiation of therapy or achievement of the LDL cholesterol goal. However, our study may inform future construction of performance measures for hyperlipidemia management. It has been argued that a possible unintended consequence of population-based quality measures is that they may penalize physicians who care for complex patients.4–9
Our findings strengthen the argument that quality measures should account for patient preferences, type of comorbidity and clinical complexity.
This study has some limitations. We examined 1,935 patients from an urban population receiving care in six primary care clinics affiliated with a single academic medical center. It is also notable that we selected a population known to be receiving poor quality care at baseline (i.e., they were known to have high LDL cholesterol, but were not taking medications). Therefore, the generalizability of observed results is limited. While all prescriptions written by primary care providers should have been documented in EPIC, we were not able to identify prescriptions written by specialists who do not use EPIC. We also were not able to identify patients managed with lifestyle interventions. To account for this discrepancy, however, we included achievement of guideline-consistent LDL cholesterol as an outcome. We used follow-up of 6 months to 2 years as our analytical time frame because it allowed clinicians adequate opportunity to institute management even in complex patients, and analyses were adjusted for number of visits per patient during the time frame. However, patients with longer follow-up periods may have presented differential opportunities to receive treatment or achieve LDL cholesterol goals. We also were not able assess cases in which patients were lost to follow-up. Some patients for whom we have incomplete data may have transitioned to an outside primary care practice before the end of the study period or may have died. As we stated above, our inability to determine severity of disease is a point that warrants further study. Another limitation was our inability to determine those patients for whom lipid-lowering therapy was absolutely contraindicated. To attempt to account for some contraindications to therapy, we excluded patients with liver disease from the analysis. Additionally, previous work has shown that few patients have documented contraindications to lipid-lowering therapy.37
We faced the challenge that NCEP ATP III guidelines19
are not clear on the best approach for management of lipids in patients older than 85 years. Because quality measurement does not consider this exception (failure to manage high LDL cholesterol in this group is still considered to be “poor quality care”), we applied guideline criteria uniformly regardless of age. Notably, less than 4% of our cohort was over the age of 85. Another limitation is that we examined the association between comorbid conditions and initiation of medication for a single target condition. The observed relationships may differ for other conditions or other types of interventions. Finally, our measure of comorbidity was not a complete measure of patient complexity because we were not able to account for other factors such as poor adherence, patient preferences, or social barriers to care.
Among our cohort of primary care patients with hypertension and elevated LDL cholesterol, the nature of the comorbid conditions was associated with the likelihood of LDL cholesterol management. Patients with an increasing number of discordant conditions were less likely to receive guideline-consistent care even in the presence of cardiovascular disease or risk equivalent. Although some patients with a strong preference to reduce medication burden or with reduced life expectancy may make a decision not to start lipid-lowering therapy, most patients, particularly those with cardiovascular disease, should be receiving guideline-consistent care for hyperlipidemia. Programs that help set priorities for the medical encounter should be considered to help focus physicians and patients on the important task of cardiovascular risk reduction.