Table of Contents

Component Description

C-reactive protein is considered one of the best measures of the acute-phase response to an infectious disease or other cause of tissue damage and inflammation. It is used to correct the iron status measures, which are affected by inflammation. It can also be used to measure the body’s response to inflammation from chronic conditions, such as arthritis, and environmental exposures to agents such as tobacco smoke.

Eligible Sample

Participants aged 3 years and older.

Description of Laboratory Methodology

Blood specimens are processed, stored and shipped to University of Washington, Seattle, WA.

This method quantified CRP by latex-enhanced nephelometry. Particle-enhanced assays were based on the reaction between a soluble analyte and the corresponding antigen or antibody bound to polystyrene particles. For the quantification of CRP, particles consisting of a polystyrene core and a hydrophilic shell were used to link anti-CRP antibodies covalently. A dilute solution of test sample was mixed with latex particles coated with mouse monoclonal anti-CRP antibodies. CRP present in the test sample forms an antigen antibody complex with the latex particles.

An automatic blank subtraction was performed. CRP concentrations were calculated by using a calibration curve. Data reduction of the signals was performed by using a storable logit-log function for the calibration curve performed data reduction of the signals. These assays were performed on a Behring Nephelometer for quantitative CRP determination.

There were no changes (from the previous 2 years of NHANES) to equipment, lab methods or lab site.

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.

Laboratory Quality Assurance and Monitoring

The NHANES quality control and quality assurance protocols (QA/QC) 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 on Laboratory Data file for detailed QA/QC protocols.

Analytic Notes

NHANES Survey Design:

The analysis of NHANES laboratory data must be conducted with the key survey design and basic demographic variables. The Demographic file contains: Status Variables providing core information on the survey participant including examination status, Recoded Demographic Variables including age, gender, race etc., and Interview and Examination Sample Weight Variables and Survey Design Variables. The Questionnaire Data Files contain socio-economic data, health indicators, and other related information collected during household interviews. The Phlebotomy Examination file includes auxiliary information on duration of fasting, the time of day of the venipuncture, and the conditions precluding venipuncture. The Demographic, Questionnaire and Phlebotomy Examination files may be linked to the laboratory data file using the unique survey participant identifier SEQN.

Detection Limits:

The lower detection limit for CRP was constant during this two-year cycle.
Serum ultra sensitive CRP= 0.02 ng/mL.

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 NHANES Analytic Guidelines and the on-line NHANES Tutorial  for further details on the use of sample weights and other analytic issues.

Codebook and Frequencies

SEQN - Respondent sequence number

Variable Name:
SAS Label:
Respondent sequence number
English Text:
Respondent sequence number.
Both males and females 3 YEARS - 150 YEARS

LBXCRP - C-reactive protein(mg/dL)

Variable Name:
SAS Label:
C-reactive protein(mg/dL)
English Text:
C-reactive protein(mg/dL)
Both males and females 3 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
0.01 to 18.01 Range of Values 8299 8299
. Missing 912 9211