Survey captures snapshot of nation's health

Even if you have never heard of the National Health and Nutrition Examination Survey -- NHANES -- some of the information that stems from it is probably right in front of you.

When a child's growth is assessed, physicians refer to charts derived from its results. When the American Medical Association and other medical societies issue scientific reports, the numbers cited often come from this data set. Studies drawing conclusions from its findings are published almost daily. Public health officials base decisions on the survey's answers and use them to determine if what they are doing is working.

"NHANES serves as a real-time repository of what's happening with health," said Georges Benjamin, MD, American Public Health Assn. executive director. "I cannot imagine doing without this kind of information."

Numerous surveys are carried out regularly, but none like this one. Organized by the Centers for Disease Control and Prevention's National Center for Health Statistics, NHANES is the only survey to use in-person interviews and direct clinic services on a nationally representative sample.

It's not a telephone poll. Researchers are not culling insurance claims data. Instead, at a cost of $35 million to the federal government, tests are done on about 7,000 people selected annually from 15 communities nationwide. More than 140,000 people have taken part since the study was first attempted, from 1960 to 1962, as the National Health Examination Survey I. It was then carried out intermittently until 1999 when it became continuous.

Each person surveyed statistically represents as many as 65,000 people.

"I love NHANES because it's a national data set. We can pursue a lot of different questions," said Martin Blaser, MD, chair of medicine and professor of microbiology at New York University. He has authored several studies using NHANES data.

In August, a set of four connected, climate-controlled trailers containing examination and survey equipment -- one of three mobile examination centers circulating the country and traveling an average of 5,000 miles every year -- is in the parking lot of the Edward Hines Jr. VA Hospital in Hines, Ill., just outside Chicago. Here it will collect data on 350 people on one of its final stops to round up the 2007-08 cohort.

The effort began even before the trailers arrived. Workers visited homes based on census data and a randomized statistical formula. Letters were sent advising residents that they would be visited by an NHANES researcher who would ask basic demographic questions. Based on their answers, people were invited to visit the trailers. They received a token payment between $30 and $100 and as much as $4,800 worth of medical testing, including various scans and analyses of blood and urine.

Patients at the trailers get weighed and measured. They also are assessed for anemia, cardiovascular disease, diabetes, environmental toxins, hearing, balance, infectious disease, kidney function, lung capacity, and nutritional status. Testing is voluntary.

"It's very good baseline information," said study manager Jacque DeMatteis. "A doctor would not order some of these tests, and participants get the benefit of all of this information while helping everyone in the U.S."

No diagnoses are made. Rather, if something appears amiss, patients are advised to seek health care. If they don't have a medical home, one is recommended. Everyone seen receives a full list of results and is encouraged to take them to their physicians.

"We have had people call in quite grateful for what we found in the health exam," said Kathryn Porter, MD, NHANES' medical officer.

The tests that are done are selected with input from numerous other government health agencies and change frequently. The survey also periodically oversamples groups to get more robust data on pressing issues. Previous studies recruited additional pregnant women to investigate folate levels. This year, the survey is calling in more older people in the hopes of helping the health system deal with the growing elderly population.

Some of the notable achievements of this survey include prompting the U.S. Dept. of Agriculture to fortify grain and cereal with iron because so many children, women of childbearing age and elderly people were deficient. NHANES also supplied early evidence that blood lead levels were too high -- prompting the phaseout of this gasoline additive.