National Health and Nutrition Examination Survey

Diabetes mellitus was assessed by measures of plasma glucose, serum insulin, and serum C-peptide in participants aged 12 years and over in the morning examination session only. Glycohemoglobin measures were available for a full sample.

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 were among people with diabetes. The prevalence of diabetes and overweight (one of the major risk factors for diabetes) continue 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. Fasting weights are available for sample persons fasting at least 8 hours or more but less than 24 hours.

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.

Insulin

Insulin radioimmunoassay (RIA) is a double-antibody batch method. Insulin in the specimen competes with a fixed amount of 125I-labelled insulin for the binding sites of the specific insulin antibodies. Bound and free insulin are separated by adding a second antibody, centrifuging, and decanting. The radioactivity in the pellet is then measured. The radioactivity is inversely proportional to the quantity of insulin in the specimen.

C-Peptide

C-peptide radioimmunoassay (RIA) is a competitive assay where ¹²⁵I-labelled 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 insulin in the specimen.

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 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.

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

NHANES 2001–2002 Laboratory Data

The analysis of NHANES 2001–2002 laboratory data must be conducted with the key survey design and basic demographic variables. The NHANES 2001–2002 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.

LBXGLU and LBXGLUSI, Plasma glucose; LBXCP and LBXCPSI, C-peptide; LBXIN and LBXINSI, Insulin

Plasma glucose, serum C-peptide and insulin 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.

The Laboratory 10 Data File which contains laboratory test results for glucose (LBXGLU) was measured using the reference analytic method. However, the Lab 40 biochemistry profiles also included measurements of this analyte. These serum glucose values (LBXSGL) reported in Lab 40 release should not be used to determine undiagnosed diabetes or prediabetes. Instead, plasma glucose values (LBXGLU) should be used based on the reference analytic method of this analyte. Use the special weights included in this data file when analyzing data.

Sampling Weights: WTSAF4YR and WTSAF2YR (4-year and 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 analyst is strongly encouraged to use the 4-year fasting weights (WTSAF4YR) to analyze 1999-2002 data for participants 12 years and older. The 2-year fasting weights (WTSAF2YR) should be used when analyzing NHANES 2001-2002. The use of the full sample MEC examined weights (WTMEC4YR or WTMEC2YR) should not be used to analyze the data if the outcome of interest is only measured on the morning fasting sample.

The recommended procedure for variance estimation requires use of stratum and PSU variables (SDMVSTRA and SDMVPSU, respectively), which are included in the demographic data file for each data release.

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

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 (Robbins et al., 1996; Volund, 1993).