National Health and Nutrition Examination Survey

Diabetes mellitus was assessed by measures of fasting plasma glucose, two-hour glucose (OGTT) and serum insulin in participants, aged 12 years and over, who were examined in the morning (AM) session only. Glycohemoglobin measures were collected in a full sample and are available in a separate dataset, GLU_F.

Diabetes is a leading cause of disease and death in the United States. Eight million Americans are known to have diabetes, and an approximately equal number have undiagnosed diabetes. In 1993, nearly 18 percent of all deaths, for persons over the age of 25, were among people with diabetes. The prevalence of diabetes and overweight (one of the major risk factors for diabetes) continues to increase. Substantial new efforts to prevent or control diabetes have begun, including the Diabetes Prevention Trial and the National Diabetes Education Program.

Diabetes testing provides population data to: 1) determine a national estimate of diabetes disease prevalence (diagnosed and undiagnosed), 2) identify the risk factors of diabetes disease; 3) permit a national cohort to be established for follow-up studies of this condition; and 4) provide critical information to clinicians and public health officials for the development of preventive care and community-based interventions.

Participants, aged 12 years and older, who were examined in the morning session and met a 9 hour fast, were eligible. This is a subsample of the NHANES and requires the use of special weights (See Analytic Notes below).

Plasma specimens were processed, stored and shipped to Fairview Medical Center Laboratory at the University of Minnesota, Minneapolis Minnesota for analysis.

Glucose concentration was determined by a hexokinase method. It is an endpoint enzymatic method with a sample blank correction.

Beginning in 2005, an oral glucose tolerance test (OGTT) was added to the laboratory protocol. A fasting glucose blood test was performed on all participants, 12 years and older, who were examined in the morning session, after a 9 hour fast. After the initial venipuncture, participants were asked to drink a calibrated dose (generally 75 grams of glucose) of TrutolTM and had a second venipuncture 2 hours (plus or minus 15 minutes) after drinking the Trutol.

There are seven exclusion criteria including hemophilia and chemotherapy safety exclusions, fasting less than 9 hours, taking insulin or oral medications for diabetes, refusing phlebotomy, and not drinking the entire Trutol solution within the allotted time.

There were no changes (from the previous 2 years of NHANES) to equipment, lab methods, or lab site.

Detailed instructions on specimen collection and processing can be found in the NHANES Laboratory/Medical Technologists Procedures Manual (LPM).

Read the General Documentation on Laboratory Data file for detailed data processing and editing protocols.

The analytical methods are described in the Description of the Laboratory Methodology section.

One calculated variable was created in this data file. The formula for its creation is as follows:

LBXGLT and LBDGLTSI:
The fasting glucose value in mg/dL (LBXGLT) was converted to mmol/L (LBDGLTSI) by multiplying by 0.05551 (rounded to 3 decimals).

The NHANES quality control and quality assurance protocols (QA/QC) meet the 1988 Clinical Laboratory Improvement Act mandates. Detailed QA/QC instructions are discussed in the NHANES Laboratory/Medical Technologists Procedures Manual (LPM). Read the General Documentation on Laboratory Data file for detailed QA/QC protocols.

NHANES Survey Design:

The analysis of NHANES laboratory data must be conducted with the key survey design and basic demographic variables. The Demographic file contains: Status Variables providing core information on the survey participant including examination status, Recoded Demographic Variables including age, gender, race etc., and Interview and Examination Sample Weight Variables and Survey Design Variables. The Questionnaire Data Files contain socio-economic data, health indicators, and other related information collected during household interviews. The Phlebotomy Examination file includes auxiliary information on duration of fasting, the time of day of the venipuncture, and the conditions precluding venipuncture. The Demographic, Questionnaire and Phlebotomy Examination files may be linked to the laboratory data file using the unique survey participant identifier SEQN.

These are new variables that should help the user in the analysis of the two-hour glucose tolerance data:

GTDSCMMN is used to define 
         "Glucose challenge Administer Time in minutes".
GTDDR1MN is used to define: 
         "Time from fast glucose & challenge (min)"
GTDBL2MN is used to define: 
         "Time from fasting glucose & OGTT(min)"
GTDDR2MN is used to define: 
         "Time from glucose challenge & OGTT(min)"
GTXDRANK is used to define: 
         "Amount of glucose challenge the SP drank"
GTDCODE is used to define: 
         "Incomplete OGTT Comment Code"

Sampling Weights
The analyst is strongly encouraged to use the OGTT sampling weights in this file to analyze 2009–2010 two-hour OGTT glucose levels.

There will be two weight variables associated with the subsample for the diabetes data. Use the fasting sample weights (WTSFA2YR) when analyzing the fasting glucose and insulin levels only. Use the OGTT sample weights (WTSOG2YR) when analyzing the insulin, fasting AND OGTT glucose levels or when analyzing ONLY OGTT glucose levels. NOTE: the fasting glucose and insulin weights and data are in a separate file (GLU_F).

When the weights were calculated pregnant women were excluded. However, they based the pregnant women’s pregnancy status on the self-report of pregnancy at the MEC and not whether they were later determined to be pregnant based on the lab test at the MEC. So there are 9 SP’s that have a ridexprg variable equal to 1 in the demographic file but they have a complete OGTT exam and have a weight.

There are 17 SPs who have an OGTT exam values but were diagnosed diabetics. Therefore for weighting purposes they were put in the post strata cell with other diagnosed diabetics. This could be problem from an analytic point of view if they are not analyzed with the other diagnosed diabetics.

Please refer to the NHANES Analytic Guidelines and the on-line NHANES Tutorial  for further details on the use of sample weights and other analytic issues.