Table of Contents

Locator Record

Title: Total Cholesterol (TCHOL_E )
Contact Number: 1-866-441-NCHS
Years of Content: 2007 - 2008
First Published: September, 2009
Revised: February, 2010
Access Constraints: None
Use Constraints: None
Geographic Coverage: National
Subject:Total Cholesterol
Record Source: NHANES 2007 - 2008
Survey Methodology: NHANES 2007 - 2008 is a stratified multistage probability sample of the civilian non-institutionalized population of the U.S.
Medium: NHANES Web site; SAS transport files

Component Description

The main element of the cardiovascular disease laboratory component in NHANES is blood lipid levels. Cardiovascular disease is the leading cause of death in the United States. The data will be used to monitor the status of hyperlipidemia and the success of the National Cholesterol Education Program.

Eligible Sample

Participants aged 6 years and older were tested.

Description of Laboratory Methodology

Blood specimens were processed, stored, and shipped to University of Minnesota, Minneapolis, MN for analysis.

Detailed specimen collection and processing instructions are discussed in the NHANES Laboratory/Medical Technologists Procedures Manual (LPM). Vials are stored under appropriate frozen (–30°C) conditions until they are shipped to University of Minnesota for testing.

There were changes (from the previous 2 years of NHANES) to equipment, lab method and lab site;

During 2005-2006 Johns Hopkins University perform the lipids testing. Beginning in 2007, the University of Minnesota performed the lipids testing.

There were changes in the instruments used to measure total cholesterol. In 2005, total cholesterol was measured enzymatically in serum using the Roche Hitachi 717. In 2006, total cholesterol was measured enzymatically in serum using the Roche Hitachi 717 and 912. In 2007, total cholesterol was measured in serum using Roche Modular P chemistry analyzer. No adjustment of values was necessary to account for the change in instrumentation for total cholesterol between 2005-2006 and 2007-2008.

Roche Modular P chemistry analyzer

In this enzymatic method, esterified cholesterol is converted to cholesterol by cholesterol esterase. The resulting cholesterol is then acted upon by cholesterol oxidase to produce cholest-4-en-3-one and hydrogen peroxide. The hydrogen peroxide then reacts with 4-aminophenazone in the presence of peroxidase to produce a colored product that is measured at 505 nm (secondary wavelength = 700 nm). The final step is known as the Trinder reaction. This method is a single reagent, endpoint reaction that is specific for cholesterol.

Cholesterol, a steroid molecule with a hydroxyl group in the C3 position, is synthesized in many types of tissue, but mainly in the liver and intestinal wall. About 75 per cent of cholesterol is newly synthesized, with the remainder originating from dietary intake. Cholesterol measurement is performed to screen for atherosclerotic risk and in the diagnosis and treatment of disorders involving elevated cholesterol as well as lipid and lipoprotein metabolic disorders.

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 Laboratory Methodology section above. One calculation variable was created in this data file. The formula for their calculation is as follows:

LBDTCSI: 

The total cholesterol in mg/dL (LBXTC) was converted to mmol/L (LBDTCSI) by multiplying by 0.02586.

Laboratory Quality Assurance and Monitoring

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 General Documentation of Laboratory Data file for detailed QA/QC protocols.

Analytic Notes

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. The Household Questionnaire Data Files also contain all survey design variables and sample weights required to analyze these data. The Phlebotomy Examination file includes auxiliary information on duration of fasting, the time of day of the venipuncture, and the conditions precluding venipuncture. The Household Questionnaire and Phlebotomy Exam files may be linked to the laboratory data file using the unique survey participant identifier SEQN.

In cases, where the result was below the limit of detection, the value for that variable is the detection limit divided by the square root of two.

Exam sample weights should be used for analyses. 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.

References

Codebook and Frequencies

SEQN - Respondent sequence number

Variable Name:
SEQN
SAS Label:
Respondent sequence number
English Text:
Respondent sequence number.
Target:
Both males and females 6 YEARS - 150 YEARS

LBXTC - Total Cholesterol (mg/dL)

Variable Name:
LBXTC
SAS Label:
Total Cholesterol (mg/dL)
English Text:
Total Cholesterol (mg/dL)
Target:
Both males and females 6 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
44 to 460 Range of Values 7387 7387
. Missing 745 8132

LBDTCSI - Total Cholesterol( mmol/L)

Variable Name:
LBDTCSI
SAS Label:
Total Cholesterol( mmol/L)
English Text:
Total Cholesterol( mmol/L)
Target:
Both males and females 6 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
1.14 to 11.9 Range of Values 7387 7387
. Missing 745 8132