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Division of Laboratory Sciences

The National Health and Nutrition Examination Surveys
(NHANES)

History

National normative values for the U.S. population are determined by CDC's National Health and Nutrition Examination Surveys (NHANES). As the statistical arm of CDC, the National Center for Health Statistics (NCHS) plays a major role in monitoring the nutritional and health status of the American population by sponsoring studies such as NHANES to assess the health of the population. These surveys have been performed by NCHS since the early 1960s, focusing on different population groups and health topics.

The DLS NHANES Laboratory was established in 1971 as the central laboratory for the survey and as an international reference laboratory for nutritional biochemistry measurements. The laboratory has collaborated with NCHS on the following surveys:

Survey participants are located in counties across the country, and these county areas or "stands" are chosen by NCHS, working in conjunction with the Census Bureau, to fit the survey sampling design. The sample for the survey is selected to represent all ages of the U.S. population.

Laboratory measurements performed during NHANES III on specimens collected from more than 30,000 people include:

• Blood levels of lead and protoporphyrin

• Urine levels of cadmium

• Serum levels of selenium, cotinine, ferritin, and iron

• Serum and red blood cell levels of folate

• Serum levels of vitamins A, B12, C, D, E

• A profile of five carotenoids and retinyl esters

• Total and ionized calcium

A complete list of analytes and detailed analytical methods for each analyte are found in the NHANES III Laboratory Manual, available for download (~ 11MB, Adobe Acrobat Reader required). Reports and manuals from the NHANES III survey are available on the NCHS website.

In collaboration with NCHS and as a part of NHANES III, DLS has established a specimen bank containing DNA samples from a representative cross-section of the U.S. population and has developed a mechanism to review proposals for using samples from the DNA bank and presented that mechanism to the NCHS Institutional Review Board.

Current Survey

NHANES 1999+ emphasizes adolescent health and the health of older Americans. To produce reliable statistics for these groups, adolescents 15-19 years old and people aged 60 years or older are oversampled. African-Americans and Hispanics are also oversampled to enable reliable estimates for these groups. Participants receive physical exams and complete a questionnaire about topics such as anemia, cardiovascular disease, diabetes, hearing loss, immunization, infectious disease, kidney disease, mental health, nutrition, obesity, oral health, osteoporosis, sexually transmitted diseases, reproductive health, and respiratory diseases.

In the field, survey personnel interviews participants in their homes to include demographic, socioeconomic, diet and health-related questions about smoking status, alcohol consumption, sexual practices, drug use, physical fitness and activity, dietary intake, health insurance availability, reproductive health, and occupation. Then each person undergoes a 4-hour examination in the mobile examination centers (MECs), including medical and dental examinations, physiological measurements, and laboratory tests. Each participant receives an individual health assessment and counseling if a problem is detected.

Data

Data are relayed to NCHS, which periodically releases the data to the general public on the NCHS website. Detailed descriptions of most of the analytical laboratory methods performed by DLS are also available on the NCHS website.

Data from NHANES participants will be used to determine the incidence of major diseases, risk factors for diseases, and nutritional status and its association with health promotion and disease prevention for the U.S. population. Previous rounds of the survey have documented the rise in the nation's obesity epidemic, detected elevated blood lead levels, and defined the difference between passive and active environmental tobacco smoke exposure. It was also recognized that women and children are at high risk for iron deficiency and anemia, and that before the fortification of certain foods with folic acid in 1998, 20% of the U.S. population was folate deficient. NHANES findings are also the basis for national standards for such measurements as height, weight, and blood pressure. Data from the survey are used in epidemiologic and health sciences research, which helps develop sound public health policy, direct and design health programs and services (such as USDA's Food Stamps, Women, Infant, and Children [WIC], and clinic programs), and expand the health knowledge for the nation.

Analytes Surveyed

The following is a sample of the analytes included in the NHANES 1999+ survey. Analytes are added and removed as the survey progresses.

In Plasma:

• Homocysteine
• Methylmalonic Acid