• Component Description
• Eligible Sample
• Description of Laboratory Methodology
• Data Processing and Editing
• Laboratory Quality Assurance and Monitoring
• Analytic Notes
• Codebook
  • SEQN - Respondent sequence number
  • WTSAF2YR - Fasting Subsample 2 Year MEC Weight
  • LBXGLU - Fasting Glucose (mg/dL)
  • LBDGLUSI - Fasting Glucose (mmol/L)
  • LBXIN - Insulin (uU/mL)
  • LBDINSI - Insulin (pmol/L)
  • PHAFSTHR - Total length of 'food fast', hours
  • PHAFSTMN - Total length of 'food fast', minutes

National Health and Nutrition Examination Survey

2007-2008 Data Documentation, Codebook, and Frequencies

Plasma Fasting Glucose & Insulin (GLU_E)

Data File: GLU_E.xpt

First Published: January 2010

Last Revised: NA

Component Description

Diabetes mellitus was assessed by measures of fasting plasma glucose, two-hour glucose (OGTT) and serum insulin in participants aged 12 years and over in the morning (AM) examination session only. Glycohemoglobin measures are also 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 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) continue to increase. Substantial new efforts to prevent or control diabetes have begun, including the Diabetes Prevention Trial and the National Diabetes Education Program.

Eligible Sample

Participants aged 12 years and older who were examined in the morning session were tested.

Description of Laboratory Methodology

Blood specimens were processed, stored and shipped to Fairview Medical Center Laboratory at the University of Minnesota, Minneapolis Minnesota for analysis. Detailed specimen collection and processing instructions are discussed in the NHANES Laboratory/Medical Technologists Procedures Manual (LPM).

Glucose
In this enzymatic method glucose is converted to glucose-6-phosphate (G-6-P) by hexokinase in the presence of ATP, a phosphate donor. Glucose-6-phosphate dehydrogenase then converts the G-6-P to gluconate-6-P in the presence of NADP+. As the NADP+ is reduced to NADPH during this reaction, the resulting increase in absorbance at 340 nm (secondary wavelength = 700 nm) is measured. This is an endpoint reaction that is specific for glucose.

Insulin
Insulin is the primary hormone responsible for controlling glucose metabolism, and its secretion is determined by plasma glucose concentration. The insulin molecule is synthesized in the pancreas as pro-insulin and is later cleaved to form C-peptide and insulin. The principal function of insulin is to control the uptake and utilization of glucose in the peripheral tissues. Insulin concentrations are severely reduced in insulin-dependent diabetes mellitus (IDDM) and some other conditions, while insulin concentrations are raised in non-insulin-dependent diabetes mellitus (NIDDM), obesity, and some endocrine disorders.

The Merocodia Insulin ELISA is a two-site enzyme immunoassay utilizing the direct sandwich technique with two monoclonal antibodies directed against separate antigenic determinants of the insulin molecule. Specimen, control, or standard is pipetted into the sample well, and then followed by the addition of peroxidase-conjugated anti-insulin antibodies. Insulin present in the sample will bind to anti-insulin antibodies bound to the sample well, while the peroxidase-conjugated anti-insulin antibodies will also bind to the insulin at the same time. After washing to remove unbound enzyme-labelled antibodies, a labelled substrate is added and binds to the conjugated antibodies. Acid is added to the sample well to stop the reaction, and the colorimetric endpoint is read on a microplate spectrophotometer set to the appropriate light wavelength.

There were changes to the equipment from NHANES 2005-2006. For NHANES 2005-2006, glucose measurements were performed on the Roche/Hitachi 911 (Roche Diagnostics, 9115 Hague Road, Indianapolis, IN 46250.) using the hexokinase assay and for NHANES 2007-2008 glucose measurements were performed on the Roche Modular P chemistry analyzer (Roche Diagnostics, 9115 Hague Road, Indianapolis, IN 46250.) using the hexokinase assay.

An oral glucose tolerance test (OGTT) continued. 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 Trutol^TM and had a second venipuncture 2 hours (plus or minus 15 minutes) after drinking the Trutol^TM.

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

A detailed description of the laboratory methods used can be found on the NHANES website.

Data Processing and Editing

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.

Two derived variables were created in this data file. The formula for their derivation is as follows:

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

LBXIN and LBDINSI:
The insulin value in µU/mL (LBXIN) was converted to pmol/L (LBDINSI) by multiplying by 6.0 (rounded to 2 decimals).

There was no recoding of data or fill values.

Laboratory Quality Assurance and Monitoring

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 LPM. Read the General Documentation on Laboratory Data file for detailed QA/QC protocols.

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

Analytic Notes

Glucose regression equations to compare 2007-2008 and 2005-2006 data:

A crossover study was performed to compare the 2007-2008 glucose data to the 2005-2006 glucose data. The Roche/Hitachi 911 was used in 2005-2006 and the Roche ModP was used in 2007-2008. A Deming regression analysis was done and the following regressions were obtained for glucose (mg/dL):

Y (Roche 911) = X (Roche ModP) – 1.139, n=143, r=0.997, slope was not significant.

Y (Roche ModP) = X (Roche 911) + 1.148, n=143, r=0.997, slope was not significant.

These regression equations should be used to trend the glucose data.

NHANES 2007-2008 Survey Design:

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

The Minnesota Laboratory Data File (GLU_E) (which contains laboratory test results for glucose - LBXGLU) was measured using the reference analytic method. However, the Iowa laboratory (BIOPRO_E), that measures biochemistry profiles, also included measurements of serum glucose. The serum glucose values (LBXSGL) reported in the Iowa lab should not be used to determine undiagnosed diabetes or prediabetes. Instead, plasma glucose values from the Minnesota Lab (LBXGLU) should be for data analysis.

Sampling Weights
The analyst is strongly encouraged to use the fasting sampling weights in this file to analyze 2007–2008 glucose and insulin levels.

There will be two weight files associated with 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 OGTT weights and data are in a separate file (OGTT_E).

Please refer to the Analytic Guidelines for further details on the use of sample weights and other analytic issues. The Analytic Guidelines are available on the NHANES website.

Codebook and Frequencies