• Component Description
• Eligible Sample
• Description of Laboratory Methodology
• Data Processing and Editing
• Laboratory Quality Assurance and Monitoring
• Analytic Notes
• Codebook
  • SEQN - Respondent sequence number
  • WTSOG2YR - OGTT Subsample 2 Year MEC Weight
  • GTDSCMMN - Glucose challenge Administer Time in min
  • GTDDR1MN - Time from fast glucose & challenge (min)
  • GTDBL2MN - Time from fasting glucose & OGTT (min)
  • GTDDR2MN - Time from glucose challenge & OGTT(min)
  • GTXDRANK - Amount of glucose challenge drank
  • PHAFSTHR - Total length of 'food fast', hours
  • PHAFSTMN - Total length of 'food fast', minutes
  • GTDCODE - Incomplete OGTT Comment Code
  • LBXGLT - Two Hour Glucose(OGTT) (mg/dL)
  • LBDGLTSI - Two Hour Glucose(OGTT) (mmol/L)

National Health and Nutrition Examination Survey

2007-2008 Data Documentation, Codebook, and Frequencies

Oral Glucose Tolerance Test (OGTT_E)

Data File: OGTT_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, who were examined in the morning (AM) session only. Glycohemoglobin measures were collected in a full sample and are available in a separate dataset, GHB_E.

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.

Eligible Sample

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).

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

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.

A detailed description of the laboratory methods for OGTT can be found in the Laboratory Procedures Manual.

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.

One calculated variable was created in this data file. The formula for its calculation 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).

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

Laboratory Quality Assurance and Monitoring

The NHANES quality control and quality assurance protocols (QA/QC) meet the 1988 Clinical Laboratory Improvement Amendments 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.

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 2007–2008 two-hour OGTT glucose levels.

There will be two weight files 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_E).

Codebook and Frequencies