National Health and Nutrition Examination Survey

See important notes for insulin and fasting weights under the Analytic Notes section below.

Diabetes mellitus was assessed by measures of plasma glucose and serum c-peptide in participants aged 12 years and older in the morning (AM) examination session only. Glycohemoglobin measures were available for a full sample for participants 12 years and older.

Diabetes is a leading cause of disease and death in the United States. Eight million Americans are known to have diabetes, and an equal number have undiagnosed diabetes. In 1993, nearly 18 percent of all deaths for persons over the age of 25 had 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.

Information on the prevalence of diabetes disease, especially in its early stages, and associated risk factors will be used to help develop early intervention and prevention programs for the disabling consequences of this condition. Specifically, the diabetes disease examination will provide population data to:

1. determine a national estimate of diabetes disease prevalence (diagnosed and undiagnosed), including those at high risk for the late complications of the disease (i.e., ulceration and amputation);
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 were tested.

Glucose

The enzyme hexokinase (HK) catalyzes the reaction between glucose and adenosine triphosphate (ATP) to form glucose-6-phosphate (G-6-P) and adenosine diphosphate (ADP). In the presence of nicotinamide adenine dinucleotide (NAD), G-6-P is oxidized by the enzyme glucose-6-phosphate dehydrogenase (G-6-PD) to 6-phosphogluconate and reduced nicotinamide adenine dinucleotide (NADH). The increase in NADH concentration is directly proportional to the glucose concentration and can be measured spectrophotometrically at 340 nm.

C-Peptide

C-peptide radioimmunoassay (RIA) is a competitive assay where 125I-labeled C-peptide competes with C-peptide in the specimen for antibody sites. Bound and free C-peptide is separated by adding a second PEG-accelerated double antibody. The antibody-bound fraction is precipitated and counted. The radioactivity is inversely proportional to the quantity of C-peptide in the specimen.

Insulin

Human insulin is a polypeptide hormone originating in the ßeta-cells of the pancreas and serving as a principal regulator for the storage and production of carbohydrates. Its secretion is normally stimulated by increases in the amount of glucose in the circulation.

The Tosoh AIA-PACK IRI is a two-site immunoenzymometric assay which is performed entirely in the AIA-PACK. Insulin present in the test sample is bound with monoclonal antibody immobilized on a magnetic solid phase and enzyme-labeled monoclonal antibody in the AIA-PACK. The magnetic beads are washed to remove unbound enzyme-labeled monoclonal antibody and are then incubated with a fluorogenic substrate, 4-methylumbelliferyl phosphate (4MUP). The amount of enzyme-labeled monoclonal antibody that binds to the beads is directly proportional to the IRI concentration in the test sample. A standard curve is constructed, and unknown sample concentrations are calculated using this curve. The amount of sample required for Tosoh insulin analysis is 25uL.

There were changes to the equipment and lab method from the previous 2 years.

Blood specimens were processed, stored and shipped to University of Missouri-Columbia, Columbia, Missouri for analysis. Detailed specimen collection and processing instructions are discussed in the NHANES LPM. Read the LABDOC file for detailed data processing and editing protocols. The analytical methods are described in the Description of the Laboratory Methodology section.

There was no top coding or derived variables in this file.

Detailed instructions on specimen collection and processing can be found on the NHANES website.

The NHANES quality assurance and quality control (QA/QC) protocols 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 LABDOC file for detailed QA/QC protocols.

A detailed description of the quality assurance and quality control procedures can be found on the NHANES website.

1. Comparison of NHANES 2003-2004 to NHANES 1999-2002 Insulin Values:
The serum insulin method changed for NHANES in 2003. A Pharmacia method (see above) was used for NHANES 1999-2002 and a Tosoh method (see above) was used for NHANES 2003-2004. The mean value for the Tosoh method was about 11% lower than the Pharmacia method mean value. Two crossover studies were performed comparing the Pharmacia to the Tosoh values on split specimens.

The following “backward” linear regression was obtained for LBXIN (µU/mL):

Pharmacia-equivalent = 0.96006 * Tosoh + 3.23663; n=245; r=0.981

The following “forward” linear regression was obtained for LBXIN (µU/mL):

Tosoh-equivalent = 1.0027 * Pharmacia - 2.2934; n=245; r=0.981

We recommend using these linear regressions to adjust the NHANES 1999-2002 Pharmacia values when comparing them to NHANES 2003-2004 insulin values.

2. Conversion factor for insulin units
The conversion factor for insulin is 1uU/mL=6.00 pmol/L. This unit conversion is based on the WHO standard adopted in 1987 based on a human insulin with a potency of 26000 U/g (1,2).

3. Survey design and basic demographic variables
The analysis of NHANES 2003–2004 laboratory data must be conducted with the key survey design and basic demographic variables.The NHANES 2003–2004 Household Questionnaire Data Files contain demographic data, health indicators, and other related information collected during household interviews. They also contain all survey design variables for these age groups. The phlebotomy file includes auxiliary information such as the conditions precluding venipuncture. The household questionnaire and phlebotomy files may be linked to the laboratory data file using the unique survey participant identifier SEQN.

4. Plasma glucose and serum c-peptide
Plasma glucose and serum c-peptide were measured by the Diabetes Diagnostic Laboratory at the University of Missouri-Columbia on participants aged 12 years and older in the morning examination session only.

5. LBXGLU and LBXSGL
The Lab 10 Data File contains laboratory test results for glucose measured using the reference analytic method. However, the lab 40 biochemistry profiles also included measurements of this analyte. The serum glucose values (LBXSGL) reported in the lab 40 release should not be used to determine undiagnosed diabetes or prediabetes. Instead, plasma glucose values (LBXGLU) from lab 10 should be used based on the reference analytic method of this analyte.

6. Sampling Weights:
WTSAF2YR (2-year fasting weights for participants 12+ years):
One-half of the participants were sampled to attend the morning session. Those participants ages 12 and older appointed to attend the morning session were instructed to fast at least 9 hours prior to their appointment time.

Subsample weights were required for analysis since the analysis of interest involves only those sampled persons ages 12 and older examined in the morning. Because fasting is a key characteristic of this subsample, this data item is called “fasting” weight. Non-zero fasting weights were generated for sample persons 12 years and older who fasted 8 to 24 hours and had plasma glucose values and diabetics who fasted but had missing plasma glucose values. Diabetics who did not fast have zero weights.

The 2-year fasting weights (WTSAF2YR) should be used when analyzing NHANES 2003-2004. The use of the full sample MEC examined weights (WTMEC2YR) should not be used to analyze the data if the outcome of interest is only measured on the morning fasting sample.

See the Analytic Guidelines regarding applying weights for analysis of data.