Sex Disparity in the Management of Dyslipidemia Among Patients With Type 2 Diabetes Mellitus in a Managed Care Organization

Objective: To determine whether there were sex-related differencesin the management of dyslipidemia among managed careenrollees with diabetes mellitus.

Study Design and Methods: Retrospective analyses were conductedusing medical and pharmacy claims data from a healthmaintenance organization during 2000 and 2001. Patients withtype 2 diabetes mellitus were identified through a validated algorithmof medication and diagnosis codes. Chi-squared analysis wasused to determine if women were less likely than men to receive alipid test or a lipid-modifying drug. Logistic regression models wereconstructed to compare sex-related differences while controllingfor age, cardiovascular disease diagnosis, and 2 proxies of illnessseverity (hospitalization in 2000 and the intensity of diabetes mellitusdrug therapy).

P

P

Results: During 2000 and 2001, 79.4% of women received alipid test compared with 84.2% of men (&#967;² = 6.69, = .01). Also,33.2% of women received a lipid-modifying drug compared with45.5% of men (&#967;² = 27.31, < .01). Logistic regression analysisrevealed that men were more likely than women to receive a lipidtest when controlling for age, cardiovascular disease diagnosis, andillness severity (odds ratio [OR], 1.45; 95% confidence interval,1.13-1.81). Men were also more likely than women to receive alipid-modifying drug when controlling for age, cardiovascular diseasediagnosis, illness severity, and lipid testing (OR, 1.51; 95%confidence interval, 1.22-1.86).

Conclusion: Women with type 2 diabetes mellitus were lesslikely than men with type 2 diabetes mellitus to receive lipid testsor lipid-modifying drugs.

(Am J Manag Care. 2005;11:69-73)

The worldwide prevalence of diabetes mellitus isincreasing, as are the demand for and the cost ofmedical care.^1-3 In 2002, there were 18.2 millionpeople (6.3% of the population) in the United States whohad diabetes mellitus.¹ The direct medical expendituresfor diabetes mellitus totaled nearly $92 billion in 2002,with cardiovascular complications comprising a substantialportion of the costs.^2,3 The prevalence of cardiovasculardisease (CVD) and its associated mortalityare substantially higher among persons with diabetesmellitus than among those without diabetes mellitus.^4,5

Studies^6-10 have examined the sex gap in CVD morbidityand mortality among persons with diabetes mellitus.A key epidemiological study⁶ of heart disease inpersons with diabetes mellitus identified that mortalityfrom coronary heart disease has been declining in menbut rising in women. Three meta-analyses^7-9 found thatthe odds ratio for CVD-related events in women withdiabetes mellitus is higher than that in men with diabetesmellitus, although the most recent meta-analysis⁹showed that the sex differences become negligible whenadjusted for CVD risk factors (eg, age, smoking, andcholesterol levels). Nonetheless, a recent study¹⁰ amongthe participants of the Framingham Heart Study foundthat the relative risk for coronary heart disease mortalityin women with diabetes mellitus is substantiallyhigher than that in men with diabetes mellitus, evenwhen controlling for the primary risk factors for coronaryheart disease.

The sex differences in CVD-related mortality may bedue to a greater number of risk factors among womenwith diabetes mellitus or a greater effect of CVD risk factorson women with diabetes mellitus.¹¹ An additionalreason may be that CVD risk factors are less aggressivelymanaged in women with diabetes mellitus comparedwith their male counterparts.¹² Researchers have identifiedsex disparities in the use of drug therapy for dyslipidemia;however, it is not clear if these disparitiesrepresent an actual sex bias in prescribing.^13,14

Guidelines from the American Diabetes Associationrecommend annual screenings for dyslipidemia in allpersons with diabetes mellitus and aggressive managementof dyslipidemia, with drug therapy initiationthresholds that are similar for men and women.^15,16 Theproportion of managed care enrollees with type 2 diabetesmellitus who are receiving drug therapy for dyslipidemiahas increased substantially in recent years.¹⁷However, it is not clear whether women with diabetesmellitus are receiving similar treatment for dyslipidemiacompared with men with diabetes mellitus. Theobjectives of this study were 2-fold: (1) to determine ifmen with type 2 diabetes mellitus were more likely tobe screened or monitored for dyslipidemia than womenwith type 2 diabetes mellitus and (2) to determine ifmen with type 2 diabetes mellitus were more likely toreceive drug therapy for dyslipidemia than women withtype 2 diabetes mellitus.

METHODS

Design and Subjects

This study used a retrospective cross-sectionaldesign examining medical and pharmacy claims datafrom the commercially insured population of a university-affiliated health maintenance organization in themidwestern United States. The study was approved bythe University of Michigan Institutional Review Board.Eligible subjects were at least 18 years of age, were continuouslyenrolled in the health plan during the entirestudy period, had more than 1 medical claim with a diabetesmellitus diagnosis, and had more than 1 claim foran oral diabetes mellitus drug. Patients using insulinwere excluded from the analyses to increase the homogeneityof the sample.

Variables

Current Procedural Terminology

Current

Procedural Terminology

International Classification of Diseases, Ninth Revision,

Clinical Modification

Drug use data were extracted from the pharmacyclaims, while laboratory tests were identified fromcodes within the medicalclaims. All the variables were recoded into categoricaldata for the purpose of statistical analysis. Adichotomous variable for lipid testing was coded as 1 ifthe patient had a medical claim containing a code for any lipid test (eg,total cholesterol, low-density lipoprotein, or lipid panel)and as 0 if the patient did not have any claims for thesetests. The lipid drug variable was coded as 1 if thepatient had at least 1 claim for any prescription lipid-modifyingdrug and as 0 if there were no claims forthese drugs. Sex was coded as 1 for male and as 0 forfemale. Age in 2000 was stratified into 4 age categories(18-44, 45-54, 55-64, and &#8805;65 years) for comparisonacross the age groups. A dichotomous variable was constructedto indicate whether the patient had a CVDdiagnosis during 2000 or 2001. The variable was codedas 1 if the patient had at least 1 medical claim with ancode for selected CVDs(an appendix listing these codes is available from theauthor). Finally, 2 proxies for severity of illness werecreated: (1) a hospitalization event in 2000 (yes or no)and (2) multiple-drug therapy versus single-drug therapyfor diabetes mellitus.

Statistical Analysis

Descriptive analyses were conducted to assess thedistribution of each variable. Bivariate comparisons oflipid testing and lipid-modifying drug use across sex categorieswere conducted using cross-tabulations and &#967;²tests. Multivariate modeling of data was done usinglogistic regression models to assess the relationship ofsex with lipid testing and lipid-modifying drug use whileadjusting for covariates such as age, CVD diagnosis, hospitalization,and multiple-drug therapy. All statisticalanalyses were performed using SPSS version 11.0 (SPSSInc, Chicago, Ill).

RESULTS

Descriptive Analysis

There were 1729 patients identified in 2000 and2001 who met the inclusion criteria. Of these, 50.1%were women and 49.9% were men. The mean age forwomen was 49 years, while the mean age for men was52 years. Among all patients, 1429 (82.6%) received alipid test in 2000 or 2001. In 2000 and 2001, 675patients (39.0%) received a lipid-modifying drug.Descriptive data for the entire sample are found inTable 1.

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P

Descriptive data regarding sex differences in the useof lipid tests and lipid-modifying drugs were evaluated.During 2000 and 2001, 79.4% of women received a lipidtest compared with 84.2% of men (&#967;² = 6.69, = .01).Also, 33.2% of women received a lipid-modifying drugcompared with 45.5% of men (&#967;² = 27.31, < .01).

Multivariate Models

Logistic regression was used to control for severalvariables that could confound the results. For model 1(dependent variable, lipid test in 2000-2001), the controlvariables included the subject's age, hospitalizationin 2000, multiple-drug therapy, and a CVD diagnosis(Table 2). When controlling for these variables, menwere 1.45 times (95% confidence interval [CI], 1.13-1.81 times) more likely than women to receive a lipidtest during 2000 or 2001.

For model 2 (dependent variable, lipid-modifyingdrug use in 2000-2001), the control variables includedthe subject's age, hospitalization in 2000, multiple-drug therapy, a CVD diagnosis, and a lipid testin 2000 or 2001 (Table 3). When controlling forthese variables, men were 1.51 times (95% CI,1.22-1.86 times) more likely than women toreceive a lipid-modifying drug during 2000 or2001.

DISCUSSION

Women with type 2 diabetes mellitus were lesslikely than men with type 2 diabetes mellitus toreceive lipid tests or lipid-modifying drugs whencontrolling for age, CVD diagnosis, and 2 proxiesfor severity of illness (hospitalization and diabetesmellitus drug intensity). The reasons forthese differences could not be determined fromclaims data alone, and the sex disparity in lipidtesting and treatment may reflect clinical differencesin the patients. However, prior researchhas shown that women with diabetes mellitus areat a higher risk of cardiovascular complicationsthan men with diabetes mellitus; thus, the disparitiesin testing and treatment warrant furtherinvestigation.^6-10

A recent study¹⁷ revealed that diabeticpatients with coronary artery disease are lesslikely to receive lipid testing or lipid-modifyingtherapy than nondiabetic persons with coronaryartery disease. Additional studies have identifiedthat women are less likely to receive diagnosticprocedures^18,19 or drug therapy^12-14 for CVD.Although women with diabetes mellitus appear tohave an elevated risk of cardiovascular morbidityand mortality compared with men with diabetesmellitus,^6-10 the present study reveals that womenare also less likely to receive lipid tests or lipid-modifyingdrugs. Therefore, women with diabetesmellitus may be at high risk for undertreatmentof CVD.

The reasons for the sex disparity in testingand treatment for CVD in patients with diabetesmellitus are not clear. It is possible that thelower rates of treatment for dyslipidemia inwomen with diabetes mellitus occur for severalreasons. Women, in general, may not be highly concernedabout heart disease and may not raise the issuewith their physicians.²⁰ Women may also experiencesymptoms of CVD that are different from those of men,and these "atypical"symptoms may not be discussedin a clinical encounter or may not prompt further evaluationof cardiovascular causes of the symptoms.²¹Middle-aged women with diabetes mellitus, or their clinicians,might also place higher priority on treatingthe symptoms of other health problems (eg, menopause).If women place higher priorities on noncardiovascularissues in discussions with their clinicians, it ispossible that cardiovascular concerns may not receiveadequate attention.

The aforementioned explanations for sex disparitymay be intertwined with the general problem of clinicalinertia (ie, failure to prescribe or intensify therapywhen indicated).²² Therefore, efforts to combat clinicalinertia (eg, physician feedback and reminder systems)could help to alleviate the sex disparities in monitoringor treating dyslipidemia in women with diabetes mellitus.²³ Specifically, reminders that prompt physicians toorder lipid tests for patients with diabetes mellitus maybe particularly helpful for women if sex disparities haveoccurred because of a greater number of competing prioritiesin clinical encounters with women. Flagging elevatedlow-density lipoprotein levels may also help tostimulate prescribing of lipid-modifying therapy whenappropriate.

Bird and colleagues²³ have suggested that sex disparitiesare an important concern in quality of care formanaged care organizations. They suggest that healthplans consider sex-stratified reporting of performancemeasures and feedback to physicians. The Women'sHealth Measurement Advisory Panel of the NationalCommittee for Quality Assurance recommends thatresearch be done to examine sex differences in healthplan performance on conditions that are highlyprevalent among men and women (eg, diabetesmellitus).²⁴ Further education of physicians onthe high risk of cardiovascular mortality inwomen with diabetes mellitus may be warranted.

It is important to note that the data used in thisstudy were derived from only the commerciallyinsured population of one health plan. Althoughthe health plan represents a large, diverse groupof patients, caution should be used in generalizingthe findings beyond the managed care population.In addition, the claims data set did not includelaboratory test results (eg, low-density lipoproteinlevels), so it is difficult to evaluate the appropriatenessof the prescribing patterns for lipid-modifyingdrugs. However, the analyses controlled forthe presence of medical claims with CVD diagnoses,age, and 2 proxies for severity of illness.

CONCLUSIONS

Women with type 2 diabetes mellitus were lesslikely than men with type 2 diabetes mellitus toreceive lipid tests or lipid-modifying drugs. Giventhe higher rate of CVD mortality among womenwith diabetes mellitus compared with men withdiabetes mellitus, the lower rate of lipid testingand lipid-modifying drug therapy for women warrantsfurther attention.

Acknowledgments

We appreciate the comments of William Herman, MD, and ThomasSpafford, MS, on early drafts of the manuscript, as well as the cooperationof M-CARE, University of Michigan, in providing the data used in this study.

From the Center for Medication Use, Policy & Economics, Department of Social andAdministrative Sciences, University of Michigan College of Pharmacy, Ann Arbor.

This work was supported by the University of Michigan Health System.Preliminary analyses from this study were presented at the 9th Annual InternationalMeeting of the Society for Pharmacoeconomics and Outcomes Research; May 18, 2004;Arlington, Va.

Address correspondence to: David P. Nau, PhD, Center for Medication Use, Policy& Economics, Department of Social and Administrative Sciences, University of MichiganCollege of Pharmacy, 428 Church Street, Ann Arbor, MI 48109-1065. E-mail:dnau@umich.edu.

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