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    <div id="toc">
      <h3>Table of Contents</h3>
      <div id="toc-scroll">
        <ul>
          <li>
            <a href="#Component_Description">Component Description</a>
          </li>
          <li>
            <a href="#Eligible_Sample">Eligible Sample</a>
          </li>
          <li>
            <a href="#Description_of_Laboratory_Methodology">Description of Laboratory Methodology</a>
          </li>
          <li>
            <a href="#Laboratory_Method_Files">Laboratory Method Files</a>
          </li>
          <li>
            <a href="#Laboratory_Quality_Assurance_and_Monitoring">Laboratory Quality Assurance and Monitoring</a>
          </li>
          <li>
            <a href="#Data_Processing_and_Editing">Data Processing and Editing</a>
          </li>
          <li>
            <a href="#Analytic_Notes">Analytic Notes</a>
          </li>
          <li>
            <a href="#References">References</a>
          </li>
          <li>
            <a href="#Codebook">Codebook</a>
            <ul id="CodebookLinks">
              <li>
                <a href="#SEQN">SEQN - Respondent sequence number</a>
              </li>
              <li>
                <a href="#LBXGH">LBXGH - Glycohemoglobin (%)</a>
              </li>
            </ul>
          </li>
        </ul>
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      <div id="PageHeader">
        <h1>National Health and Nutrition Examination Survey</h1>
        <h2>2017-2018 Data Documentation, Codebook, and Frequencies</h2>
        <h3>Glycohemoglobin (GHB_J)</h3>
        <h4> Data File: GHB_J.xpt</h4>
        <h5 class="left">First Published: February 2020</h5>
        <h5 class="right">Last Revised: NA</h5>
      </div>
      <div id="Sections">
        <h2 id="Component_Description">Component Description</h2><p style="margin: 0in 0.5in 12pt; line-height: 15.95pt;">In 2015, diabetes was
the seventh leading cause of death in the United States. &nbsp;More than 30 million Americans are living with
diabetes, and 86 million are living with prediabetes, which is a serious health
condition that increases a person&rsquo;s risk of type 2 diabetes and other chronic
diseases. The prevalence of diabetes and overweight (one of the major risk
factors for diabetes) continue to increase. Substantial new efforts to prevent
or control diabetes have begun, including the Diabetes Prevention Trial and the
National Diabetes Education Program. </p>
<p style="margin: 0in 0.5in 12pt; line-height: 15.95pt;">Diabetes testing
provides population data to: 1) determine a national estimate of diabetes
prevalence (diagnosed and undiagnosed); 2) identify the risk factors; 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. </p><h2 id="Eligible_Sample">Eligible Sample</h2><p style="margin: 0in 0.5in 12pt; line-height: 15.95pt;">Examined
participants aged 12 years and older were eligible.</p><h2 id="Description_of_Laboratory_Methodology">Description of Laboratory Methodology</h2><p style="margin: 0in 0.5in 12pt; line-height: 15.95pt;">In this assay, the
stable (SA1c) and labile (LA1c) A1c forms can be individually resolved on the
chromatogram without manual pretreatment, allowing accurate measurement of the
stable form of HbA1c. The analyzer dilutes the whole blood specimen with a
hemolysis solution, and then injects a small volume of the treated specimen
onto the HPLC analytical column. Separation is achieved by utilizing differences
in ionic interactions between the cation exchange group on the column resin
surface and the hemoglobin components. The hemoglobin fractions (A1c, A1b, F,
LA1c, SA1c, A0 and H-Var) are subsequently removed from the column material by
step-wise elution using elution buffers each with a different salt
concentration. The separated hemoglobin components pass through the photometer
flow cell where the analyzer measures changes in absorbance at 415 nm. The
analyzer integrates and reduces the raw data, and then calculates the relative
percentages of each hemoglobin fraction. Analysis requires three minutes. If a
specimen showed a deterioration peak, hemoglobin variant, or a LA1c results &ge;
5% and/or LA1c results &gt; half SA1c during the regular test, it would be retested
by a second method, <span style="font-family: Calibri;">ultra 2 HPLC</span>. In the 2017-2018 cycle, only 2.2% of the blood specimens required to be
retested by the <span style="font-family: Calibri;">ultra 2 HPLC</span> method. A lab instrumentation change was made for this secondary
method during the data collection period. This instrument change did not
significantly affect the resulted glycohemoglobin values; the mean relative
error between results from the two instruments was 0.5% (ranged from -4.0% to
5.2%).</p>
<p style="margin: 0in 0.5in 12pt; line-height: 15.95pt;">Refer to the
Laboratory Method Files section for a detailed description of the laboratory
methods used.</p>
<p style="margin: 0in 0.5in 12pt; line-height: 15.95pt;">Other than the
minor change in the secondary <span style="font-family: Calibri;">ultra 2
HPLC</span> method described above, there were no
changes to the lab method, lab equipment, or lab site for this component in the
NHANES 2017-2018 cycle.</p><h2 id="Laboratory_Method_Files">Laboratory Method Files</h2>
        <p>
          <a target="_blank" href="https://wwwn.cdc.gov/nchs/data/nhanes/public/2017/labmethods/GHB-J-Premier-508.pdf">Glycohemoglobin_Premier</a>
          <span> (February 2020)</span>
        </p>
        <p>
          <a target="_blank" href="https://wwwn.cdc.gov/nchs/data/nhanes/public/2017/labmethods/GHB-J-G8-508.pdf">Glycohemoglobin_G8</a>
          <span> (February 2020)</span>
        </p>
        <h2 id="Laboratory_Quality_Assurance_and_Monitoring">Laboratory Quality Assurance and Monitoring</h2><p style="margin: 0in 0.5in 12pt; line-height: 15.95pt;">Whole blood specimens
were processed, stored, and shipped to the University of Missouri-Columbia, MO
for analysis. </p>
<p style="margin: 0in 0.5in 12pt; line-height: 15.95pt;">Detailed
instructions on specimen collection and processing are discussed in the NHANES <a href="https://wwwn.cdc.gov/nchs/data/nhanes/public/2017/manuals/2017_MEC_Laboratory_Procedures_Manual.pdf">Laboratory Procedures Manual (LPM)</a>. Vials are stored under appropriate&nbsp;refrigerated (2-8&deg;C) conditions
until they were shipped to University of Missouri for testing.</p>
<p style="margin: 0in 0.5in 12pt; line-height: 15.95pt;">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 <a href="https://wwwn.cdc.gov/nchs/data/nhanes/public/2017/manuals/2017_MEC_Laboratory_Procedures_Manual.pdf">NHANES LPM</a>.</p>
<p style="margin: 0in 0.5in 12pt; line-height: 15.95pt;"><b>Mobile Examination
Centers (MECs)</b> <br />
Laboratory team performance is monitored using several techniques. NCHS and contract
consultants use a structured competency assessment evaluation during visits to
evaluate both the quality of the laboratory work and the quality control
procedures. Each laboratory staff&nbsp;member is observed for equipment
operation, specimen collection and preparation; testing procedures and
constructive feedback are given to each staff member. Formal retraining
sessions are conducted annually to ensure that required skill levels were
maintained. </p>
<p style="margin: 0in 0.5in 12pt; line-height: 15.95pt;"><b>Analytical
Laboratories</b> <br />
NHANES uses several methods to monitor the quality of the analyses performed by
the contract laboratories. In the MEC, these methods include performing blind
split samples collected on &ldquo;dry run&rdquo; sessions. In addition, contract
laboratories randomly perform repeat testing on 2% of all specimens.</p>
<p style="margin: 0in 0.5in 12pt; line-height: 15.95pt;">NCHS developed and
distributed a quality control protocol for all CDC and contract laboratories,
which outlined the use of Westgard rules (Westgard et al., 1981) when running
NHANES specimens. Progress reports containing any problems encountered during
shipping or receipt of specimens, summary statistics for each control pool, QC
graphs, instrument calibration, reagents, and any special considerations are submitted
to NCHS quarterly. The reports are reviewed for trends or shifts in the data.
The laboratories are required to explain any identified areas of concern.</p><h2 id="Data_Processing_and_Editing">Data Processing and Editing</h2><p style="margin: 0in 0.5in 12pt; line-height: 15.95pt;">The data were
reviewed. Incomplete data or improbable values were sent to the performing
laboratory for confirmation. </p><h2 id="Analytic_Notes">Analytic Notes</h2><p style="margin: 0in 0.5in 12pt; line-height: 15.95pt;">Refer to the <a href="https://wwwn.cdc.gov/nchs/nhanes/continuousnhanes/overviewlab.aspx?BeginYear=2017">2017 - 2018 Laboratory Data Overview</a> for general information on NHANES laboratory data.</p>
<p style="margin: 0in 0.5in 12pt; line-height: 15.95pt;">There are over 800 laboratory tests performed on NHANES participants. However, not all participants provided biospecimens or enough volume for all the tests to be performed. The specimen availability can also vary by age or other population characteristics. For example, in 2017-2018, approximately 80% of children aged 1-17 years who were examined in the MEC provided a blood specimen through phlebotomy, while 95% of examined adults age 18 and older provided a blood specimen. Analysts should evaluate the extent of missing data in the dataset related to the outcome of interest as well as any predictor variables used in the analyses to determine whether additional re-weighting for item non-response is necessary.</p>
<p style="margin: 0in 0.5in 12pt; line-height: 15.95pt;">Please refer to
the NHANES <a href="https://www.cdc.gov/nchs/nhanes/survey_methods.htm">Analytic Guidelines</a> and the on-line NHANES <a href="https://wwwn.cdc.gov/nchs/nhanes/tutorials/">Tutorial</a> for further
details on the use of sample weights and analytic issues. </p>
<p style="margin: 0in 0.5in 12pt; line-height: 15.95pt;"><b>Demographic and
Other Related Variables</b> </p>
<p style="margin: 0in 0.5in 12pt; line-height: 15.95pt;">The analysis of
NHANES laboratory data must be conducted using the appropriate survey design
and demographic variables. The <a href="https://wwwn.cdc.gov/nchs/nhanes/search/datapage.aspx?Component=Demographics&amp;CycleBeginYear=2017">NHANES 2017-2018 Demographics File</a> contains demographic data, health indicators, and other related
information collected during household interviews as well as the sample design
variables. The recommended procedure for variance estimation requires use of
stratum and PSU variables (SDMVSTRA and SDMVPSU, respectively) in the
demographic data file. </p>
<p style="margin: 0in 0.5in 12pt; line-height: 15.95pt;">The <a href="https://wwwn.cdc.gov/nchs/data/nhanes/public/2017/datafiles/fastqx_j.htm">Fasting Questionnaire File</a> includes auxiliary information, such as fasting status, length of fast and
the time of venipuncture. </p>
<p style="margin: 0in 0.5in 12pt; line-height: 15.95pt;">This laboratory
data file can be linked to the other NHANES data files using the unique survey
participant identifier (i.e., SEQN). </p>
<p style="margin: 0in 0.5in 12pt; line-height: 15.95pt;"><b>Detection Limits </b></p>
<p style="margin: 0in 0.5in 12pt; line-height: 15.95pt;">Since
this data is reported in percent, the use of lower LLODs isn&rsquo;t applicable. <br style="mso-special-character: line-break;" />
</p></div>
      <div id="References">
        <h2>References</h2>
        <ul>
          <li>Centers for Disease Control and Prevention. National Diabetes Statistics Report: Estimates of Diabetes and Its Burden in the United States, 2014. Atlanta, GA: U.S. Department of Health and Human Services; 2014.</li>
          <li>Westgard J.O., Barry P.L., Hunt M.R., Groth T. A multi-rule Shewhart chart for quality control in clinical chemistry. Clin Chem (1981) 27:493-501.</li>
        </ul>
      </div>
      <div id="Codebook">
        <h2>Codebook and Frequencies</h2>
        <div class="pagebreak">
          <h3 class="vartitle" id="SEQN">SEQN - Respondent sequence number</h3>
          <dl>
            <dt>Variable Name: </dt>
            <dd class="info">SEQN</dd>
            <dt>SAS Label: </dt>
            <dd>Respondent sequence number</dd>
            <dt>English Text: </dt>
            <dd class="info">Respondent sequence number.</dd>
            <dt>Target: </dt>
            <dd> Both males and females 12 YEARS -
			150 YEARS</dd>
          </dl>
        </div>
        <div class="pagebreak">
          <h3 class="vartitle" id="LBXGH">LBXGH - Glycohemoglobin (%)</h3>
          <dl>
            <dt>Variable Name: </dt>
            <dd class="info">LBXGH</dd>
            <dt>SAS Label: </dt>
            <dd>Glycohemoglobin (%)</dd>
            <dt>English Text: </dt>
            <dd class="info">Glycohemoglobin (%)</dd>
            <dt>Target: </dt>
            <dd> Both males and females 12 YEARS -
			150 YEARS</dd>
          </dl>
          <table class="values">
            <thead>
              <tr>
                <th scope="column" class="values">Code or Value</th>
                <th scope="column" class="values">Value Description</th>
                <th scope="column" class="values">Count</th>
                <th scope="column" class="values">Cumulative</th>
                <th scope="column" class="values">Skip to Item</th>
              </tr>
            </thead>
            <tbody>
              <tr>
                <td scope="row" class="values">3.8 to 16.2</td>
                <td class="values">Range of Values</td>
                <td class="values" align="right">6045</td>
                <td class="values" align="right">6045</td>
                <td class="values">
                </td>
              </tr>
              <tr>
                <td scope="row" class="values">.</td>
                <td class="values">Missing</td>
                <td class="values" align="right">356</td>
                <td class="values" align="right">6401</td>
                <td class="values">
                </td>
              </tr>
            </tbody>
          </table>
        </div>
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