The data will be used to monitor the status of hyperlipidemia and the success of the National Cholesterol Education Program.
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.
Participants aged 6 years and older were tested.
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).
In this method a magnesium/dextran sulfate solution is first added to the specimen to form water-soluble complexes with non-HDL cholesterol fractions. These complexes are not reactive with the measuring reagents added in the second step. With addition of reagent 2, HDL-cholesterol esters are converted to HDL-cholesterol by PEG-cholesterol esterase. The HDL-cholesterol is acted upon by PEG-cholesterol oxidase, and the hydrogen peroxide produced from this reaction combines with 4-amino-antipyrine and HSDA under the action of peroxidase to form a purple/blue pigment that is measured photometrically at 600 nm (secondary wavelength = 700 nm). When the cholesterol measuring enzymes are modified with PEG, they are preferentially more reactive with HDL-cholesterol than the other cholesterol fractions. This is an endpoint reaction that is specific for HDL-cholesterol. This 3rd generation method differs from 2nd generation assays in the type of buffer used in the reagents, and the concentration of the reagent components. The basic reaction principle is unchanged.
There were changes (from the previous 2 years of NHANES) to equipment, and lab site. The lab method was essentially the same. Read the following for these changes:
From 1999-2006 Johns Hopkins University performed the testing. The equipment used was the Hitachi 717 and Hitachi 912. (Roche Diagnostics, 9115 Hague Road, Indianapolis, IN 46250)
From 2007--2008 the University of Minnesota performed the testing. The equipment used was the Roche Modular P chemistry analyzer. (Roche Diagnostics, 9115 Hague Road, Indianapolis, IN 46250).
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 derived variable was created in this data file. The formula for its derivation is as follows:
LBDHDDSI:
The HDL-cholesterol in mg/dL (LBXHDD) was converted to mmol/L (LBDHDDSI) by multiplying by 0.02586
There is no recoding of data or fill values.
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.
Change in Assay Methods Most Likely Responsible for Changes in HDL Cholesterol values in NHANES 1999-2008
Researchers are cautioned to interpret trends in HDL cholesterol for NHANES 1999-2008 in view of probable HDL cholesterol method effects. The mean HDL cholesterol values from 1999-2008 showed changes for sample participants 20 years or older:
| Years | n | Mean HDL*(mg/dL) | SEM** |
|---|---|---|---|
| 1999-2000 | 4117 | 50.6 | 0.7 |
| 2001-2002 | 4691 | 51.9 | 0.28 |
| 2003-2004 | 4475 | 54.1 | 0.38 |
| 2005-2006 | 4481 | 54.6 | 0.36 |
| 2007-2008 | 5332 | 51.9 | 0.53 |
* Weighted mean to account for complex sample design of NHANES
**SEM is the standard error of the mean
The changes in average HDL Cholesterol levels from 1999-2008 were seen across various age, gender and race-ethnicity groups indicating a method effect. The HDL cholesterol was analyzed in 1999-2002 using two methods - heparin manganese precipitation and a direct HDL immunoassay depending on the participant age and amount of specimen. Most participants in 1999-2002 were measured by the precipitation method. Starting in 2003, all HDL cholesterol samples were analyzed using the direct HDL cholesterol immunoassay method. The heparin-manganese precipitation method and direct immunoassay method for 1999-2000, 2001-2002 and 2005-2006 showed an undesirable bias (>4%) when compared to the laboratory's HDL-cholesterol quality controls (Solomon Park Research Laboratories, Kirkland, WA) that were assigned values established by the Centers for Disease Control and Prevention. The CDC HDL cholesterol reference method uses heparin-manganese to precipitate HDL-cholesterol and the Abell-Kendall method to measure cholesterol. The HDL cholesterol for 1999-2000, 2001-2002 and 2005-2006 were adjusted using:
Corrected HDL = [(Solomon Park assigned HDL value) x (Participant HDL)] / (Quality Control HDL value associated with participant sample)]
The bias for the HDL cholesterol method for 2003-2004 was acceptable (<4%) and the participant results were not corrected. In addition, there was a change in instrumentation in 2005-2006 and there were several modifications of the direct HDL cholesterol method. To control for these differences in methods and instrumentation, the HDL cholesterol was corrected using the Solomon Lab quality controls as described above. In 2007-2008, a new laboratory performed the HDL cholesterol using a direct HDL cholesterol method similar to the direct HDL method of 2005-2006, but it was performed on a different instrument.
Both laboratories performing HDL Cholesterol from 1999-2008 participated in the CDC-NHLBI Lipid Standardization Program (LSP). The CDC LSP maximum allowable bias for HDL Cholesterol is 5%. The average bias compared to the reference CDC HDL Cholesterol value for 2007-2008 was approximately -0.5%. The average bias compared to the CDC HDL Cholesterol values for 2003-2004 and 2005-2006 were approximately +2.7% and +2.0%, respectively. Unfortunately, the HDL Cholesterol values for the LSP program for 1999-2002 could not be evaluated. This indicates that the 2007-2008 HDL Cholesterol values may be less biased than the 2003-2006 values; however, both laboratories were within the 5% maximum allowable bias for HDL Cholesterol.
The changes in average HDL Cholesterol levels from 1999-2008 were seen across various age, gender and race-ethnicity groups indicating a method effect. Other covariates (body mass index, medications, physical exercise, and smoking and alcohol consumption) may explain some of the changes in HDL cholesterol, but it is unlikely to account for the majority of the mean changes in HDL cholesterol.
General 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. They also contain all survey design variables and sample weights 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.
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.
| Code or Value | Value Description | Count | Cumulative | Skip to Item |
|---|---|---|---|---|
| 7 to 155 | Range of Values | 7387 | 7387 | |
| . | Missing | 745 | 8132 |
| Code or Value | Value Description | Count | Cumulative | Skip to Item |
|---|---|---|---|---|
| 0.18 to 4.01 | Range of Values | 7387 | 7387 | |
| . | Missing | 745 | 8132 |