Table of Contents

Locator Record

Title: Second Day Exam on C-reactive protein, etc. (L11_2_R )
Contact Number: 1-866-441-NCHS
Years of Content: 2000 - 2000
First Published: July, 2010
Revised: NA
Access Constraints: RDC Only
Use Constraints: RDC Only
Geographic Coverage: National
Subject:The second-day examination on C-reactive protein (CRP), Fibrinogen, Bone Alkaline Phosphatase and Urinary N-telopeptides
Record Source: NHANES 2000 - 2000
Survey Methodology: NHANES 2000 - 2000 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

See the general documentation on second day laboratory exams. Also, see the documentation for the primary exam data for Lab 11 C-Reactive Protein.

C-reactive protein (CRP)
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.

Fibrinogen (FB)
Fibrinogen is an essential blood-clotting factor and is involved in a range of other functions, including platelet aggregation and smooth muscle proliferation. A growing body of evidence has identified fibrinogen as an important risk factor for cardiovascular disease, the major cause of death in the U.S. The objective of including this measure is to provide data on laboratory, clinical, and socio- demographic correlates of fibrinogen levels. Of particular importance in NHANES, the data will be used to study the relationship between fibrinogen levels and clinically measured lower extremity arterial blood flow as assessed by the Ankle-Brachial Index in the Lower Extremity Disease component.

Bone alkaline phosphatase (BAP) and Urinary N-telopeptides (NTx)
To assist in the evaluation of skeletal status, two markers of bone turnover are being measured: a) bone alkaline phosphatase, a formative marker in serum, and b) NTx, a resorptive marker in urine.

Eligible Sample

C-reactive protein (CRP) , Bone alkaline phosphatase (BAP), and Urinary N-telopeptides (NTx): Participants aged 16-69 years.

Fibrinogen: Participants aged 40-69 years

Description of Laboratory Methodology

C-reactive protein (CRP)
This method quantifies C-reactive protein (CRP) by latex-enhanced nephelometry. Particle-enhanced assays are 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 are used in order to link anti-CRP antibodies covalently. A dilute solution of test sample is mixed with latex particles coated with mouse monoclonal anti-CRP antibodies. CRP present in the test sample will form an antigen-antibody complex with the latex particles.

Fibrinogen (FB)
On the STA-Compact, the fibrinogen concentration in plasma is determined quantitatively by the Clauss clotting method. This test method involves measuring the rate of fibrinogen to fibrin conversion in diluted sample under the influence of excess thrombin. Since under these conditions the fibrinogen content is rate limiting, the clotting time can be used as a measure of the concentration of the fibrinogen and in fact, the clotting time is inversely proportional to the level of fibrinogen in the plasma.

Clot detection by the STA-Compact involves an electromagnetic- mechanical system. The oscillation of a steel ball within the cuvette with the thrombin and diluted plasma is monitored by the STA-Compact. When the oscillation of the steel ball is stopped by clot formation, the sensor registers the time in seconds. The time is translated into fibrinogen concentration from a fibrinogen standard curve, stored on the STA Compact.

Bone alkaline phosphatase (BAP)
The Tandem-MP Ostase ImmunoEnzymetric Assay is an in vitro device for the quantitative measurement of Skeletal Alkaline Phosphatase (sALP), an indicator of osteoblastic activity, in human serum. This device is intended to be used as an aid in the management of postmenopausal osteoporosis and Paget’s disease.

The Ostase Assay is a solid phase, monoclonal antibody immnumoenzymetric assay. Samples containing sALP are reacted with a solution containing a biotin- labeled, sALP-specific monoclonal antibody. The reaction takes place in a plastic well strip (solid phase) coated with strepavidin and enclosed in a plastic frame. Following the formation of a solid phase/capture antibody/sALP complex, the microplate is washed to remove unbound sALP and is then incubated with an enzyme substrate. The amount of substrate turnover is determined colorimetrically by measuring the absorbance of the quenched reaction at 405 nm in a microplate reader. The absorbance is proportional to the concentration of sALP present in the test sample. The calculation of sALP concentration in the sample is based on concurrent testing of sALP Calibrators and the Zero Diluent/Calibrator.

The Ostase assay is an in vitro device for the quantitative measurement of skeletal alkaline phosphatase (sALP) in human serum. Changes in sALP have been shown to be useful in participants undergoing therapy for metabolic bone disorders. It may also be an indicator of vitamin D deficiency in some participants.

Urinary N-telopeptides (NTx)
Osteomark is a competitive inhibition enzyme linked solid-phase immunosorbent assay for the quantitative measurement of the cross-linked N-telopeptides of typeI bone collagen (NTx) in human urine. The solid phase consists of microwells onto which cross-linked telopeptides (antigen) is adsorbed. Urine controls, test samples and calibrators are added to the antigen coated 96 well plate. Antibody to the N-telopeptide cross-links that are conjugated to horseradish peroxidase is then added to each well. During an initial incubation period, antigen in the sample competes with the solid phase antigen for binding to the antibody. The wells are then washed to remove unbound material.

Buffered substrate/chromogen reagent is then added to each well. During the final incubation, a blue color will develop when bound antibody-horseradish peroxidase conjugate is present in the well. The color intensity is a measure of the amount of conjugated antibody bound to the solid phase antigen, and is inversely proportional to the amount of antigen in the test sample. The reaction is stopped by the addition of stopping reagent (1N sulfuric acid) which results in a color change from blue to yellow. The absorbance values for the control, calibrators and test samples are determined spectrophotometrically at 450 nm with a 650 nm reference filter, by using a microtiter plate reader.

A standard curve is constructed for each assay by plotting absorbance versus concentration for each calibrator. The antigen concentrations of the samples and control are then read from the curve. Assay values are standardized to an equivalent amount of bone collagen, and are expressed in nanomoles bone collagen equivalents (nM BCE/L) per liter. Often assay results are corrected for urinary dilution by urinary creatinine analysis and expressed in nanomoles bone collagen equivalents per liter (nM BCE/L) per millimole creatinine per liter (mM creatinine/L). This ratio is reported as nM BCE/mM creatinine.

The discovery of urinary cross-linked N-telopeptides of type I collagen (NTx) has provided a specific biochemical marker of human bone resorption. The NTx molecule is specific to bone due to the unique amino acid sequences and orientation of the cross-linked alpha-2 N-telopeptide. Generation of the NTx molecule is mediated by osteoclasts on bone, and is found in the urine as a stable end product of degradation.

Data Processing and Editing

Blood specimens are processed, stored and shipped to University of Washington, Seattle, Washington. Detailed specimen collection and processing instructions are discussed in the NHANES Laboratory/Medical Technologists Procedures Manual (LPM). Read the LABDOC file for detailed data processing and editing protocols. The analytical methods are described in the Description of laboratory section.

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 Laboratory/Medical Technologists Procedures Manual (LPM). Read the LABDOC file for detailed QA/QC protocols.

Analytic Notes

Bone alkaline phosphatase (BAP)
Use of regression equation to trend 1999-2000 Bone alkaline phosphatase (BAP) data with 2001-2004 BAP data:

Adjustment of Bone alkaline phosphatase was necessary for NHANES 2001 data because of a change of laboratory methods between 2001 (using a Hybritech method) and 2002 (using a Beckman Access method) The distributions of sample person results were compared between NHANES 2001 and NHANES 2002 and the BAP test had significantly (p < 0.05) different means. A cross-over study between the two methods was performed to establish regression equations to convert NHANES 2001 values to NHANES 2002 equivalent values. The regression equations were applied to the BAP test, and a t test was done after regression that showed no significant differences of BAP test means between the two methods after regression. The regression equations were derived from a spline technique using logarithm-transformed BAP values. The following regression equation was obtained:

x = log(lbxbap);
lb2bap = exp(-0.5326 + 1.1139*x - 0.7963*(max(0, x-4.5151)) +0.9660*(max(0,x-4.9030)));

where lbxbap is the BAP (ug/L) value from the 1999-2001 Hybritech method and lb2bap is the BAP (ug/L) equivalent value for the 2002-2004 Beckman Access method. The analyst may wish to use this equation to trend the 1999-2004 BAP data.

The second day exam data was a convenience sample and thus did not have sample weights. The analysis of NHANES 1999-2000 laboratory data must be conducted with the key survey design and basic demographic variables. The NHANES 1999-2000 Household Questionnaire Data Files contain demographic data, health indicators, and other related information collected during household interviews. The phlebotomy file includes auxiliary information such 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.

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 16 YEARS - 69 YEARS

LB2DAY - Days between 1st and 2nd exam

Variable Name:
LB2DAY
SAS Label:
Days between 1st and 2nd exam
English Text:
Days between 1st and 2nd exam
Target:
Both males and females 16 YEARS - 69 YEARS
Code or Value Value Description Count Cumulative Skip to Item
6 to 51 Range of Values 305 305
. Missing 0 305

LB2BAP - Bone alkaline phosphotase (ug/L)

Variable Name:
LB2BAP
SAS Label:
Bone alkaline phosphotase (ug/L)
English Text:
Bone alkaline phosphotase (ug/L)
Target:
Both males and females 16 YEARS - 69 YEARS
Code or Value Value Description Count Cumulative Skip to Item
6.6 to 68.8 Range of Values 299 299
. Missing 6 305

LB2CRP - C-reactive protein(mg/dL)

Variable Name:
LB2CRP
SAS Label:
C-reactive protein(mg/dL)
English Text:
C-reactive protein(mg/dL)
Target:
Both males and females 16 YEARS - 69 YEARS
Code or Value Value Description Count Cumulative Skip to Item
0.01 to 10.1 Range of Values 300 300
. Missing 5 305

LB2FB - Fibrinogen (mg/dL)

Variable Name:
LB2FB
SAS Label:
Fibrinogen (mg/dL)
English Text:
Fibrinogen (mg/dL)
Target:
Both males and females 40 YEARS - 69 YEARS
Code or Value Value Description Count Cumulative Skip to Item
222 to 719 Range of Values 145 145
. Missing 160 305

LB2FBSI - Fibrinogen (g/L)

Variable Name:
LB2FBSI
SAS Label:
Fibrinogen (g/L)
English Text:
Fibrinogen (g/L)
Target:
Both males and females 40 YEARS - 69 YEARS
Code or Value Value Description Count Cumulative Skip to Item
2.22 to 7.19 Range of Values 145 145
. Missing 160 305

UR2NT - N-telopeptides (nmol BCE)

Variable Name:
UR2NT
SAS Label:
N-telopeptides (nmol BCE)
English Text:
N-telopeptides (nmol BCE)
Target:
Both males and females 16 YEARS - 69 YEARS
Code or Value Value Description Count Cumulative Skip to Item
21 to 11205 Range of Values 300 300
. Missing 5 305