Adherence to Lipid-lowering Therapy and Use of Preventive Health Services
Adherence to Lipid-lowering Therapy and Use of Preventive Health Services
Patients who adhere to preventive therapies may be more likely to engage in a broad spectrum of behaviors consistent with a healthy lifestyle. Because many of these behaviors cannot be measured easily, observational studies of outcomes associated with the long-term use of preventive therapies are subject to the so-called "healthy user bias." To better understand this effect, the authors examined the association between adherence to statin therapy and the use of preventive health services in a Pennsylvania cohort of 20,783 new users of statins between 1996 and 2004. After adjustment for age, gender, and various comorbid conditions, patients who filled two or more prescriptions for a statin during a 1-year ascertainment period were more likely than patients who filled only one prescription to receive prostate-specific antigen tests (hazard ratio (HR) = 1.57, 95% confidence interval (CI): 1.17, 2.19), fecal occult blood tests (HR = 1.31, 95% CI: 1.12, 1.53), screening mammograms (HR = 1.22, 95% CI: 1.09, 1.38), influenza vaccinations (HR = 1.21, 95% CI: 1.12, 1.31), and pneumococcal vaccinations (HR = 1.46, 95% CI: 1.17, 1.83) during follow-up. These results suggest that patients who adhere to chronic therapies are more likely to seek out preventive health services, such as screening tests and vaccinations. Further work is needed to identify study design and analysis methods that can be used to minimize the healthy user bias in studies of preventive therapies.
A recent meta-analysis of 21 randomized clinical trials found that patients who were adherent to placebo had lower rates of mortality than did other patients in the placebo arm who were less adherent. One explanation for this intriguing finding is that adherence to treatment is a surrogate marker for a healthy lifestyle. Thus, patients who take their medication as prescribed are more likely to engage in a broad spectrum of health-promoting behaviors that lower the risk of mortality. Because many of these behaviors may not be measured easily and others may not even be known to the investigator, observational studies of the benefits of preventive therapies may be confounded by unmeasured healthy behaviors that are related to both the treatment and study outcome.
The tendency of healthier patients to be more likely to initiate a preventive therapy leads to a bias that has been termed the "healthy user effect" or "healthy user bias". This could occur through either selective prescribing of preventive medications to patients in better health and/or through more health conscious patients seeking out prescriptions for such medications. When healthier patients are more likely to adhere to a therapy, the bias has been termed the "healthy-adherer effect", "adherence bias", or "compliance bias". In this paper, we refer to these effects collectively as the healthy user effect or healthy user bias. The biases generated by these effects may lead to spurious or exaggerated protective associations between preventive drug use and adverse clinical outcomes.
The healthy user bias has been suggested as an explanation for the discrepancy between several experimental and observational studies, including studies of the effects of long-term use of estrogen therapy and vitamin E. It has also been discussed as a potential source of bias in observational studies of the effectiveness of influenza vaccines in the elderly and the association between use of 5-hydroxy-3-methylglutaryl-coenzyme A reductase inhibitors (statins) and reduced risk of hip fracture, Alzheimer's disease, sepsis, and cancer.
Despite an increasing awareness of the potential importance of the healthy user effect, there has been little effort to study it directly. In the present research, we sought to uncover evidence of a healthy user effect among new users of statins, widely used cholesterol-lowering medications. We hypothesized that patients starting statin therapy vary in their "health-seeking" tendencies, with the more health-conscious patients being both more likely to adhere to their statin regimen and also more likely to seek out other preventive health services. To explore the plausibility of our hypothesis, we examined the association between adherence to statins and the use of various prevention-oriented health services. We conducted our analysis in a large population-based new user cohort in Pennsylvania.
Patients who adhere to preventive therapies may be more likely to engage in a broad spectrum of behaviors consistent with a healthy lifestyle. Because many of these behaviors cannot be measured easily, observational studies of outcomes associated with the long-term use of preventive therapies are subject to the so-called "healthy user bias." To better understand this effect, the authors examined the association between adherence to statin therapy and the use of preventive health services in a Pennsylvania cohort of 20,783 new users of statins between 1996 and 2004. After adjustment for age, gender, and various comorbid conditions, patients who filled two or more prescriptions for a statin during a 1-year ascertainment period were more likely than patients who filled only one prescription to receive prostate-specific antigen tests (hazard ratio (HR) = 1.57, 95% confidence interval (CI): 1.17, 2.19), fecal occult blood tests (HR = 1.31, 95% CI: 1.12, 1.53), screening mammograms (HR = 1.22, 95% CI: 1.09, 1.38), influenza vaccinations (HR = 1.21, 95% CI: 1.12, 1.31), and pneumococcal vaccinations (HR = 1.46, 95% CI: 1.17, 1.83) during follow-up. These results suggest that patients who adhere to chronic therapies are more likely to seek out preventive health services, such as screening tests and vaccinations. Further work is needed to identify study design and analysis methods that can be used to minimize the healthy user bias in studies of preventive therapies.
A recent meta-analysis of 21 randomized clinical trials found that patients who were adherent to placebo had lower rates of mortality than did other patients in the placebo arm who were less adherent. One explanation for this intriguing finding is that adherence to treatment is a surrogate marker for a healthy lifestyle. Thus, patients who take their medication as prescribed are more likely to engage in a broad spectrum of health-promoting behaviors that lower the risk of mortality. Because many of these behaviors may not be measured easily and others may not even be known to the investigator, observational studies of the benefits of preventive therapies may be confounded by unmeasured healthy behaviors that are related to both the treatment and study outcome.
The tendency of healthier patients to be more likely to initiate a preventive therapy leads to a bias that has been termed the "healthy user effect" or "healthy user bias". This could occur through either selective prescribing of preventive medications to patients in better health and/or through more health conscious patients seeking out prescriptions for such medications. When healthier patients are more likely to adhere to a therapy, the bias has been termed the "healthy-adherer effect", "adherence bias", or "compliance bias". In this paper, we refer to these effects collectively as the healthy user effect or healthy user bias. The biases generated by these effects may lead to spurious or exaggerated protective associations between preventive drug use and adverse clinical outcomes.
The healthy user bias has been suggested as an explanation for the discrepancy between several experimental and observational studies, including studies of the effects of long-term use of estrogen therapy and vitamin E. It has also been discussed as a potential source of bias in observational studies of the effectiveness of influenza vaccines in the elderly and the association between use of 5-hydroxy-3-methylglutaryl-coenzyme A reductase inhibitors (statins) and reduced risk of hip fracture, Alzheimer's disease, sepsis, and cancer.
Despite an increasing awareness of the potential importance of the healthy user effect, there has been little effort to study it directly. In the present research, we sought to uncover evidence of a healthy user effect among new users of statins, widely used cholesterol-lowering medications. We hypothesized that patients starting statin therapy vary in their "health-seeking" tendencies, with the more health-conscious patients being both more likely to adhere to their statin regimen and also more likely to seek out other preventive health services. To explore the plausibility of our hypothesis, we examined the association between adherence to statins and the use of various prevention-oriented health services. We conducted our analysis in a large population-based new user cohort in Pennsylvania.
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