Screening for Lipid Disorders Among Adults — National Health and Nutrition Examination Survey, United States, 2005–2008

Cathleen D. Gillespie, MS1

Nora L. Keenan, PhD1

James B. Miner, MPH, MA2

Yuling Hong, MD, PhD1

1Division for Heart Disease and Stroke Prevention, National Center for Chronic Disease Prevention and Health Promotion

2Financial Management Office, Office of the Chief Operating Officer

Corresponding author: Cathleen D. Gillespie, National Center for Chronic Disease Prevention and Health Promotion, CDC, 4770 Buford Hwy, MS F-72, Atlanta, GA 30341. Telephone: 770-488-5855; Fax: 770-488-8334; E-mail: CGillespie@cdc.gov.

Introduction

Cardiovascular disease (CVD) is the leading cause of preventable death in the United States (1), a major contributor to adult disability (2), and one of the most expensive conditions treated in U.S. hospitals (3). Lipid disorders (e.g., high blood cholesterol and triglycerides) increase the risk for atherosclerosis, which can lead to coronary heart disease (CHD), which accounts for a substantial proportion of cardiovascular mortality (1). Screening for lipid abnormalities is essential in detecting and properly managing lipid disorders early in the atherogenic process, thereby preventing the development of atherosclerotic plaques and minimizing existing plaques. Based on evidence-based studies, the United States Preventive Services Task Force (USPSTF) concluded that lipid measurement can identify asymptomatic adults who are eligible for cholesterol-lowering therapy (4).

According to USPSTF, the preferred screening tests for dyslipidemia or lipid disorders are total cholesterol (TC) and high-density lipoprotein cholesterol (HDL-C) on fasting or nonfasting samples. Screening recommendations are classified as having a rating of A (strongly recommended) or B (recommended) on the basis of sex, age, and risk factors for CHD (Box). USPSTF also stated that a complete fasting lipoprotein panel (i.e., TC, HDL-C, low-density lipoprotein cholesterol [LDL-C] and triglycerides [TG]) is useful for persons with dyslipidemia identified through TC and HDL-C screening tests, although they did not specify the numerical cut-points for determining lipid disorders (4). According to USPSTF, reasonable screening intervals include every 5 years with shorter or longer intervals depending on screening results (4).

In addition to the USPSTF guidelines, lipid disorder screening recommendations also have been published by the National Cholesterol Education Program (NCEP) (5), which recommends a complete fasting lipoprotein profile (TC, LDL-C, and TG) for all adults aged ≥20 years as the preferred screening test. In general, NCEP recommends target levels for fasting TC of <200 mg/dL, HDL-C of >60 mg/dL, TG of <100 mg/dL, and LDL-C of <100 mg/dL. NCEP treatment goals focus on LDL-C and vary depending on a history of, or the risk for, developing CHD: <100 mg/dL for those considered at high risk, <130 mg/dL for those considered at intermediate risk, and <160 mg/dL for those considered at low risk.

Recent population-based reports on the prevalence of screening for lipids (6), lipid levels (7,8), and the prevalence, treatment, and control of high LDL-C using NCEP CHD risk categories have been published (9), but these reports did not address the outcomes in terms of USPSTF lipid disorder screening recommendations, i.e., by the groups recommended or eligible for screening.

This report analyzes 2005–2008 data from the National Health and Nutrition Examination Survey (NHANES) to determine what proportion of the adult population should be screened for cholesterol based on the USPSTF recommendations, the prevalence of lipid screening among those for whom screening is recommended, and the prevalence of high LDL-C, LDL-C treatment and control by screening recommendation category. The results of this report will provide baseline estimates that researchers can use to track potential improvement over time in lipid screening as well as progress in LDL cholesterol treatment and control among those who are at increased risk for CVD.

Methods

To determine 1) the percentage of adults aged ≥20 years within each USPSTF-recommended screening category determined by sex, age, and CHD risk factors (0 or ≥1); 2) the prevalence of lipid screening within the previous 5 years by sex, age, and USPSTF screening category; 3) the percentage of those within each USPSTF screening category for whom a fasting full lipid panel would be useful based on the NCEP guidelines for fasting or nonfasting mean TC or HDL-C; and 4) the prevalence, treatment, and control of high LDL-C within each USPSTF screening category, CDC analyzed 2005–2008 NHANES data.

NHANES is a nationally representative cross-sectional survey of the health and nutritional status of the U.S. civilian, noninstitutionalized population (10). Although NHANES data are collected continuously, the data are released in 2-year cycles. The survey includes a household interview and a detailed physical examination. A subsample of study participants is selected randomly, and participants are asked to fast before the physical examination. Participants are included in the fasting subsample if they have fasted for 8–24 hours before blood is drawn for lipid testing. NHANES data were aggregated and analyzed from two survey periods (2005–2006 and 2007–2008). During 2005–2008, the overall survey response rate for adults aged ≥20 years was 70.8%; 10,480 adults aged ≥20 years took part in the home interviews and were examined at NHANES mobile examination centers. After exclusion of participants who were pregnant or for whom needed data were missing, the examination sample comprised 8,485 adults and the fasting sample comprised 3,427 adults.

Participants were classified into USPSTF-recommended sex, age, and risk categories for lipid screening. In accordance with USPSTF guidelines and available NHANES data, participants with one or more of the following conditions were assessed as having an increased risk for CHD: diabetes (ever told they had diabetes, fasting glucose of ≥126 mg/dL, or glycohemoglobin [A1C] of ≥6.5%), personal history of CHD (ever told they had CHD, heart attack, or angina), family history of heart attack or angina before age 50 years in close relatives (blood relatives including father, mother, sisters, or brothers), current cigarette smoking (self-reported smoking every day or some days or a measured serum cotinine level of >10 ng/mL), hypertension (an average of up to three blood pressure measurements of ≥140/90 mmHg or self-reported current use of antihypertensive medication), and obesity (body mass index [weight (kg)/height (m)2) ≥30). Detailed methods for using 2005–2008 NHANES data to categorize persons by level of CHD risk into one of the three NCEP risk groups for LDL-C–lowering therapy have been described elsewhere (9). In addition to estimating the proportion of the sample within each USPSTF recommendation group, researchers estimated the prevalence of cholesterol screening and the prevalence of TC ≥200 mg/dL or HDL-C <40 mg/dL. The prevalence, treatment, and control of high LDL-C were estimated by sex and screening recommendation group among the fasting subsample. Treatment was defined as self-reported use of cholesterol-lowering medication among those with high LDL-C; prevalence of control was defined as having a fasting LDL-C below the NCEP treatment goals, depending on CHD risk, and was calculated among all persons with high LDL-C.

National estimates and 95% confidence intervals were calculated using SAS-callable SUDAAN (Research Triangle Institute, Research Triangle Park, North Carolina) and applying appropriate survey statistical weights for the examination sample or the fasting subsample to account for the probability of selection and nonresponse. Univariate chi-square tests of independence were used to assess differences in prevalence between the screening recommendation groups. Tests were considered statistically significant at the p<0.01 level.

Results

According to the USPSTF guidelines, 88.7% of the U.S. adult population aged ≥20 years should be screened for lipid abnormalities (Table 1). The USPSTF recommendation for screening applies to 94.4% of all adult men, including 76.2% of adult men being eligible under the grade A recommendation and 17.8% being eligible under the grade B recommendation. Among all adult women, the recommendation for screening applies to 82.5%, including 52.0% being eligible under the grade A recommendation and 30.5% being eligible under the grade B recommendation. The grade A recommendation applies to the majority of adults aged ≥20 years (64.8%), with the remaining 23.9% for whom screening is recommended being eligible under the grade B recommendation. Among adults for whom screening is recommended, 70.1% reported having their cholesterol checked within the previous 5 years. Two thirds (66.6%) of men for whom screening is recommended reported having their cholesterol checked within the previous 5 years; the prevalence among women recommended for screening was 74.4%. The prevalence of cholesterol screening was higher among those who were eligible under either the grade A or grade B recommendation compared with those for whom no recommendation is made (70.1% versus 55.6%, respectively; p<0.01); this pattern was observed among both men and women. The prevalence of screening was higher among the grade A–eligible participants than it was among the grade B–eligible participants (77.7% versus 49.3%, respectively; p<0.01); this pattern also was observed in both men and women. Although the prevalence of elevated TC or low HDL-C was higher among those eligible for lipid screening based on the USPSTF recommendations, 42.7% of those to whom the screening recommendations do not apply had cholesterol levels indicating that a full fasting lipid panel would be warranted. The prevalence of high TC or low HDL-C among men not eligible for screening under the USPSTF recommendations was 39.7%, and among women not eligible for screening the prevalence was 43.8%.

The prevalence of high LDL-C (LDL-C greater than the NCEP goal or current lipid-lowering medication use) was higher among those for whom screening is recommended, compared with those for whom the recommendations do not apply (40.5% versus 13.7%, respectively; p<0.01) (Table 2). This significant difference also was observed among women (41.6% versus 17.4%, respectively; p<0.01). The prevalence of high LDL-C also was higher among the grade A–eligible participants compared with the grade B–eligible participants (48.8% versus 18.0%, respectively; p<0.01); this pattern also was observed among both men and women. The prevalence of treatment among those with high LDL-C was higher among those eligible for screening compared with those not eligible for screening (47.0% versus 37.3%, respectively; p<0.01). A similar pattern was observed among women (50.1% among those eligible for screening versus 46.1% among those not eligible for screening; p<0.01); however, the difference between men recommended for screening compared with men not recommended for screening could not be assessed as a result of small cell sizes and unstable estimates. A statistically significant difference was noted in prevalence of treatment observed between those in the grade A recommendation group compared with the grade B recommendation (51.2% for grade A versus 16.6% for grade B; p<0.01). Sample sizes did not allow for comparisons in treatment prevalence between the specific recommendation grades within genders. The prevalence of LDL-C control was significantly lower among all persons with high LDL-C for whom screening is recommended compared with those for whom screening is not recommended (33.2% versus 37.2%, respectively), and this pattern also was observed among women (34.0% among those eligible for screening versus 45.9% among those not eligible for screening; p<0.01). Sample sizes did not allow for comparisons in LDL-C control prevalence between the specific recommendation grades.

Discussion

The findings in this report indicate that 88.7% of U.S. adults aged ≥20 years are eligible for cholesterol screening per the USPSTF guidelines and that 68.4% of those eligible for screening reported being screened for cholesterol during the previous 5 years. National Health Interview Survey data for 2008 indicated that 74.6% of adults aged ≥18 years reported having had their blood cholesterol checked within the preceding 5 years (6). The distribution of persons into USPSTF groups by recommended lipid disorder screening status indicated that the highest percentages of persons screened (77.7%) were found in the two categories with a grade A recommendation (men aged ≥35 years and women aged ≥45 years at increased risk for CHD). On the basis of lipid levels, persons not recommended for lipid disorder screening were classified appropriately using the USPSTF guidelines. Similarly, a study using USPSTF recommendations to assess the proportion of persons exceeding their NCEP LDL-C goals indicated that 88% of the persons not recommended for screening had LDL-C levels at NCEP goals (11). A full lipid panel based on TC or HDL-C values would be useful for a sizeable proportion of participants in the groups not recommended for screening. Rates of treatment for high LDL-C cholesterol do not appear to be higher among those for whom screening is recommended compared with those that fall outside the criteria for recommended screening, indicating a potential need for improvement in treatment among patients at an increased risk for CHD.

Adults without health insurance are less likely than those with insurance to be tested for high cholesterol, and, if they have high cholesterol, they are less likely to receive a diagnosis and have their high cholesterol under control (12). Implementation of the provision in the Patient Protection and Affordable Care Act of 2010 (as amended by the Healthcare and Education Reconciliation Act of 2010 and referred to collectively as the Affordable Care Act [ACA]) (ACA §1001) that eliminates cost sharing for those persons enrolled in new plans who meet the USPSTF lipid disorder screening grade A and B recommendations would identify persons at increased risk for CHD who would benefit from early detection of lipid disorders and early management of lipid disorders (13). Starting in 2014, these services will be covered at no cost sharing by newly qualified private health plans operating in state-based insurance exchanges.* Moreover, beginning in 2013, state Medicaid programs that eliminate cost sharing for these clinical preventive services will receive enhanced federal matching funds for them (ACA §4106) (13,14). In addition, the Affordable Care Act ensures that preventive and wellness services be provided without cost-sharing to Medicare recipients (ACA §4104), a group comprising persons most in need of lipid management. However, recommendations for follow-up and lipid-lowering management after screening are not included in the USPSTF recommendations (15).

The findings in this report are subject to at least three limitations. First, this report might underestimate lipid levels of the U.S. population because NHANES does not include persons living in institutions such as nursing homes, and the prevalence of lipid disorders increases with age. Second, persons who received a diagnosis of a lipid disorder were not excluded from the study; the percentage of persons who were eligible for screening might be overestimated because the classification of participants was not restricted to asymptomatic persons when determining the USPSTF sex, age, and CHD risk groups or the lipid levels. Finally, using the cut-points of TC ≥200 mg/dL or HDL-C <40 mg/dL to estimate the percentage of persons for whom a full lipid panel would be useful is based on a combination of USPSTF and NCEP guidelines. USPSTF recommends complete lipid testing based on fasting or nonfasting TC or HDL levels without providing specific cut-points for estimating CHD risk. NCEP includes these cut-points but indicates that they are to be used when a fasting measure is not available. However, the combined measure has value for estimating the prevalence of being referred for a full lipid profile by USPSTF screening categories.

Conclusion

Approximately 70% of the U.S. adult population who meet the criteria for lipid screening reported having their cholesterol checked within the last 5 years, a percentage that is well below the Healthy People 2020 target of 82.1%. Because the Affordable Care Act reduces cost sharing for lipid screening, monitoring the prevalence of lipid screening among adults who meet the USPSTF or NCEP criteria is needed to determine if screening increases over time. Because lowering LDL cholesterol is associated with a decrease in the onset of subsequent CHD, and because the effectiveness of LDL-C drug therapy is well established, monitoring the treatment and control of LDL cholesterol in the population also will be important as a measure of improvements intended by the Affordable Care Act.

References

1. Kochanek KD, Xu JQ, Murphy SL, Miniño AM, Kung HC. Deaths: preliminary data for 2009. Natl Vital Stat Rep; vol 59 no 4. Available at http://www.cdc.gov/nchs/data/nvsr/nvsr58/nvsr58_19.pdf. Accessed May 17, 2012.
2. CDC. Prevalence and most common causes of disability among adults—United States, 2005. MMWR 2009;58:421–6.
3. Wier LM, Andrews RM. The national hospital bill: the most expensive conditions by payer, 2008. HCUP Statistical Brief No. 107. Rockville, MD: Agency for Healthcare Research and Quality; 2011.
4. Agency for Healthcare Research and Quality. Screening for lipid disorders in adults. Available at http://www.uspreventiveservicestaskforce.org/uspstf/uspschol.htm. Accessed May 17, 2012.
5. National Institutes of Health. Third report of the National Cholesterol Education Program (NCEP) expert panel on detection, evaluation, and treatment of high blood cholesterol in adults (Adult Treatment Panel III). Executive summary. NIH Publication No. 01-3670. Available at http://www.nhlbi.nih.gov/guidelines/cholesterol/atp3sum.pdf. Accessed May 17, 2012.
6. CDC. Healthy people 2020. Heart disease and stroke. Available at http://www.healthypeople.gov/2020/topicsobjectives2020/objectiveslist.aspx?topicId=21. Accessed May 17, 2012.
7. Cohen JD, Cziraky MJ, Cai Q, Wallace A, et al. 30-year trends in serum lipids among United States Adults: results from the National Health and Nutrition Examination Surveys II, III, and 1999–2006. Am J Cardiol 2010;106:969–75.
8. Carroll MD, Lacher DA, Wolz M, Sorlie PD. 30-year trends in serum lipids among United States Adults: results from the National Health and Nutrition Examination Surveys II, III, and 1999–2006. Am J Cardiol 2011:107;1868–70.
9. CDC. Vital signs: prevalence, treatment, and control of high levels of low-density lipoprotein cholesterol—United States, 1999–2002 and 2005–2008. MMWR 2011;60:109–14.
10. CDC. National Health and Nutrition Examination survey data. Available at http://www.cdc.gov/nchs/nhanes/nhanes_questionnaires.htm. Accessed May 17, 2012.
11. Persell SD, Lloyd DM, Baker DW. Implications of changing national cholesterol educations program goals for the treatment and control of hypercholesterolemia. J Gen Intern Med 2006;21:171–6.
12. Schober SE, Makuc DM, Zhang C, Kennedy-Stephenson J, Burt V. Health insurance affects diagnosis and control of hypercholesterolemia and hypertension among adults aged 20–64: United States, 2005–2008. NCHS data brief, no.57. Hyattsville, MD: US Department of Health and Human Services, CDC, National Center for Health Statistics; 2011.
13. Patient Protection and Affordable Care Act of 2010. Pub. L. No. 114–48 (March 23, 2010), as amended through May 1, 2010. Available at http://www.healthcare.gov/law/full/index.html. Accessed May 17, 2012.
14. Koh HK, Sebelius KG. Promoting prevention through the Affordable Care Act. New Engl J Med 2010;363:1296–9.
15. US Department of the Treasury, US Department of Labor, US Department of Health and Human Services. Interim final rules for group health plans and health insurance issuers relating to coverage of preventive services under the Patient Protection and Affordable Care Act §147.130. Coverage of preventive services. Available at http://www.healthcare.gov/law/resources/regulations/prevention/regs.html. Accessed May 17, 2012.>.