• Component Description
• Eligible Sample
• Description of Laboratory Methodology
• Laboratory Quality Assurance and Monitoring
• Data Processing and Editing
• Analytic Notes
• Codebook
  • SEQN - Respondent sequence number
  • WTSA2YR - Subsample A weights
  • LBXT3F - Triiodothyronine (T3), free (pg/mL)
  • LBXT4F - Thyroxine, free (ng/dL)
  • LBDT4FSI - Thyroxine, free (pmol/L)
  • LBXTGN - Thyroglobulin (ng/mL)
  • LBDTGNSI - Thyroglobulin (ug/L)
  • LBXATG - Thyroglobulin antibodies (IU/mL)
  • LBXTSH1 - Thyroid stimulating hormone (uIU/mL)
  • LBDTSH1S - Thyroid stimulating hormone (mIU/L)
  • LBXTPO - Thyroid perioxidase antibodies (IU/mL)
  • LBXTT3 - Triiodothyronine (T3), total (ng/dL)
  • LBDTT3SI - Triiodothyronine (T3), total (nmol/L)
  • LBXTT4 - Thyroxine, total (T4) (ug/dL)

National Health and Nutrition Examination Survey

2011-2012 Data Documentation, Codebook, and Frequencies

Thyroid Profile (THYROD_G)

Data File: THYROD_G.xpt

First Published: January 2014

Last Revised: October 2014

Component Description

The Thyroid Profile consists of a battery of several tests for the measurement of thyroid function, including Total and Free Thyroxine, Total and Free Triiodothyronine, Thyroglobulin, Thyroglobulin Antibodies, Thyroid Peroxidase Antibodies, and Thyroid Stimulating Hormone. Thyroid function is crucial for maintaining normal metabolic function in adults and for proper neurological development of the fetus. Serum levels will be used to assess thyroid function and will provide population-based reference information on these hormone levels.

Eligible Sample

Examined participants aged 12 years and older from a one-third sample.

Description of Laboratory Methodology

Thyroid blood specimens were processed, stored and shipped to Collaborative Laboratory Services, Ottumwa, Iowa. Detailed specimen collection and processing instructions are discussed in the NHANES Laboratory Procedures Manual (LPM).

Thyroid-stimulating hormone

The Access HYPERsensitive human thyroid-stimulating hormone (hTSH) assay is a 3^rd generation, two-site immunoenzymatic (“sandwich”) assay. A sample is added to a reaction vessel with goat anti-hTSH-alkaline phosphatase conjugate, buffered protein solution, and paramagnetic particles coated with immobilized mouse monoclonal anti-hTSH antibody. (Goat anti-mouse antibody is used to immobilize the mouse anti-hTSH antibody.) The hTSH binds to the immobilized monoclonal anti-hTSH on the solid phase while the goat anti-hTSH-alkaline phosphatase conjugate reacts with a different antigenic site on the hTSH. After incubation in a reaction vessel, materials bound to the solid phase are held in a magnetic field while unbound materials are washed away. Then, the chemiluminescent substrate Lumi-Phos™ 530 is added to the vessel and light generated by the reaction is measured with a luminometer. The light production is directly proportional to the concentration of human thyroid-stimulating hormone in the sample. The amount of analyte in the sample is determined from a stored, multi-point calibration curve.

Human TSH is one of several glycoprotein hormones consisting of two non-covalently bound peptide chains: an a-chain, which is nearly identical in all, and a ß-chain, which is responsible for immunological and biological specificity. These similarities result in varying degrees of cross-reactivity of different antisera. The Access HYPERsensitive hTSH assay has virtually no cross-reactivity with other peptide hormones. The sensitivity and specificity of this test enable better discrimination between hyperthyroid and euthyroid patients.

Refer to NHANES 2011-2012 Lab Methods for Thyroid Stimulating Hormone (TSH) for detailed description of the laboratory method used.

Total T3 assay

The Access Total T3 assay is a competitive binding immunoenzymatic assay. Sample is added to a reaction vessel with a stripping agent to dissociate T3 from the binding proteins. T3 in the sample competes with the T3 analogue coupled to biotin for anti-T3 alkaline phosphatase conjugate. Of the resulting antigen/antibody complexes, the T3 analogue/antibody complexes are bound to the streptavidin coated solid phase. Separation in a magnetic field and washing removes the sample T3/antibody complexes and other materials not bound to the solid phase. Then, the chemiluminescent substrate Lumi-Phos™ 530 is added to the vessel and light generated by the reaction is measured with a luminometer. The light production is inversely proportional to the concentration of total T3 in the sample. The amount of analyte in the sample is determined from a stored, multi-point calibration curve.

Refer to NHANES 2011-2012 Lab Methods for Total Triiodothyronine, Total T3 for detailed description of the laboratory method used.

Free T3 assay

Access Free T3 assay is a competitive binding immunoenzymatic assay. A sample is added to a reaction vessel with an anti-T3 monoclonal antibody conjugated to alkaline phosphatase. During the incubation, free T3 in the sample reacts with the anti-T3 antibody. Particles coated with streptavidin and biotinylated T3 analog are then added to the mixture. Unoccupied binding sites on the anti-T3 antibody are bridged to the particle through the T3 analog. After incubation in a reaction vessel, materials bound to the solid phase are held in a magnetic field while unbound materials are washed away. Then, the chemiluminescent substrate Lumi-Phos™ 530 is added to the vessel and light generated by the reaction is measured with a luminometer. The light production is inversely proportional to the concentration of free T3 in the sample. The amount of analyte in the sample is determined from a stored, multi-point calibration curve.

Refer to NHANES 2011-2012 Lab Methods for Free Triiodothyronine, Free T3 for detailed description of the laboratory method used.

Total T4 assay

The Access Total T4 assay is a competitive binding immunoenzymatic assay. A sample is added to a reaction vessel with anti-thyroxine antibody, thyroxine-alkaline phosphatase conjugate, and paramagnetic particles coated with goat anti-mouse capture antibody and a stripping agent to dissociate all T4 from binding proteins. Thyroxine in the sample competes with the thyroxine-alkaline phosphatase conjugate for binding sites on a limited amount of specific anti-thyroxine antibody. Resulting antigen: antibody complexes bind to the capture antibody on the solid phase. After incubation in a reaction vessel, materials bound to the solid phase are held in a magnetic field while unbound materials are washed away. Then, the chemiluminescent substrate Lumi-Phos™ 530 is added to the vessel and light generated by the reaction is measured with a luminometer. The light production is inversely proportional to the concentration of thyroxine in the sample. The amount of analyte in the sample is determined from a stored, multi-point calibration curve.

Refer to NHANES 2011-2012 Lab Methods for Total Thyroxine, Total T4 for detailed description of the laboratory method used.

Free T4 assay

The Access Free T4 (FRT4) assay is a two-step enzyme immunoassay. Monoclonal anti-Thyroxine (T4) antibody coupled to biotin, sample, buffered protein solution, and streptavidin-coated solid phase are added to the reaction vessel. During this first incubation, the anti-T4 antibody coupled to biotin binds to the solid phase and the free T4 in the sample. After incubation in a reaction vessel, materials bound to the solid phase are held in a magnetic field while unbound materials are washed away. Next, buffered protein solution and triiodothyronine (T3)-alkaline phosphatase conjugate are added to the reaction vessel. The T3-alkaline phosphatase conjugate binds to the vacant anti-T4 antibody binding sites. After incubation in a reaction vessel, materials bound to the solid phase are held in a magnetic field while unbound materials are washed away. Then, the chemiluminescent substrate Lumi-Phos™ 530 is added to the vessel and light generated by the reaction is measured with a luminometer. The light production is inversely proportional to the concentration of free T4 in the sample. The amount of analyte in the sample is determined from a stored, multi-point calibration curve.

Refer to NHANES 2011-2012 Lab Methods for Free Thyroxine (Free T4) for detailed description of the laboratory method used.

Thyroglobulin (Tg) assay

The Access thyroglobulin (Tg) assay is a simultaneous one-step "sandwich" assay. A sample is added to a reaction vessel, along with biotinylated mixture of four monoclonal anti-Tg antibodies, streptavidin coated paramagnetic particles, and monoclonal anti-Tg antibody alkaline phosphatase conjugate. The biotinylated antibodies and the serum or plasma thyroglobulin bind to the solid phase, while the conjugate antibody reacts with a different antigenic site on the thyroglobulin molecule. After incubation in a reaction vessel, materials bound to the solid phase are held in a magnetic field while unbound materials are washed away. A chemiluminescent substrate, Lumi-Phos** 530 is added to the reaction vessel and light generated by the reaction is measured with a luminometer. The light production is directly proportional to the concentration of thyroglobulin in the sample. The amount of Thyroglobulin in the sample is determined by means of a stored, multi-point calibration curve.

Refer to NHANES 2011-2012 Lab Methods for Thyroglobulin, (TGN) for detailed description of the laboratory method used.

Thyroglobulin antibody assay (TgAb)

The Access thyroglobulin antibody assay is a sequential two-step immunoenzymatic "sandwich" assay. A sample is added to a reaction vessel with paramagnetic particles coated with the thyroglobulin protein. After incubation, materials bound to the solid phase are held in a magnetic field while unbound materials are washed away. The thyroglobulin-alkaline phosphatase conjugate is added and binds to the TgAb. After a second incubation, the reaction vessel is washed to remove unbound materials. A chemiluminescent substrate, Lumi-Phos™ 530 is added to the reaction vessel and light generated by the reaction is measured with a luminometer. The light production is proportional to the concentration of Thyroglobulin antibody in the sample. The amount of Thyroglobulin antibody in the sample is determined by means of a stored, multi-point calibration curve.

Refer to NHANES 2011-2012 Lab Methods for Thyroglobulin Antibodies for detailed description of the laboratory method used.

Thyroid peroxidase antibody

The Access TPO antibody (TPOAb) assay is a sequential two-step immunoenzymatic "sandwich" assay. A sample is added to a reaction vessel with paramagnetic particles coated with the thyroid peroxidase protein. After an incubation, materials bound to the solid phase are held in a magnetic field while unbound materials are washed away. The protein A-alkaline phosphatase conjugate is added and binds to the TPOAb. After a second incubation, the reaction vessel is washed to remove unbound materials. A chemiluminescent substrate, Lumi-Phos™ 530 is added to the reaction vessel and light generated by the reaction is measured with a luminometer. The light production is proportional to the concentration of TPO antibody in the sample. The amount of TPOAb in the sample is determined by means of a stored, multi-point calibration curve.

Refer to NHANES 2011-2012 Lab Methods for Thyroid Peroxidase Antibodies for detailed description of the laboratory method used.

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 Procedures Manual (LPM).

Data Processing and Editing

The data were reviewed. Incomplete data or improbable values were sent to the performing laboratory for confirmation.

Four variables in this data file were created. The formula for their creation is as follows:

• Free thyroxine results in ng/dL (LBXT4F) were multiplied by 12.9 and converted into pmol/L as LBDT4FSI.
• Thyroglobin results in ng/mL (LBXTGN) were multiplied by 1.0 and converted into µg/L as LBDTGNSI.
• Thyroid stimulating hormone results in µIU/mL (LBXTSH1) were multiplied by 1.0 and converted into mIU/L as LBDTSH1S.
• Total triiodothyronine results in ng/dL (LBXTT3) were multiplied by .0154 and converted into nmol/L as LBDTT3SI.

Analytic Notes

2011-2012 Thyroglobulin Antibody:

The Beckman Coulter Access Thyroglobulin Antibody (TgAb) II assay was reformulated in January 2012 to correct for lot-to-lot variability by adding an additional buffer to the reagents (Beckman Coulter B14000A memo). Forty six specimens using the previous TgAb kit were re-analyzed using the reformulated TgAb kit. Deming regression (y=reformulated kit, x=old kit) was performed and a non-significant slope of 0.96 and a significant intercept of -0.54 IU/mL was obtained. The Pearson correlation coefficient was 0.998. A comparison of participant TgAb values analyzed with the old kit (n=1419) and with the reformulated kit (n=6144) at a cut-point of 4.0 IU/mL showed the following:

Kit         Negative (<4.0)         Positive (>=4.0)
Old                 93.2%                     6.84%
Reformulated   92.7%                     7.32%

The Chi-Square was not significant (p=.52) indicating the proportion of positive TgAb results for the old and reformulated kits were not statistically different.

Hence, no correction was necessary to adjust TgAb values during 2011-2012.

2011-2012 Total Thyroxine:

In 2009-2010, there was a change in laboratories performing the total thyroxine (TT4). The TT4 was performed at the University of Washington Medical Center, Department of Laboratory Medicine in 2009 and the TT4 was performed at the Collaborative Laboratory Services (CLS) in 2010. Both laboratories used a competitive binding immunoenzymatic assay on the Beckman Coulter Access 2 analyzer. A crossover study of 113 specimens was performed between the two laboratories and the CLS laboratory values had a higher mean and median compared to the University of Washington by approximately 5%. This was also seen in the sample participants when comparing 2009 and 2010 TT4 distributions. The difference in TT4 results may have been due to different lots of calibrators and reagents. Using a fractional polynomial regression, the 2010 TT4 participant results were lowered to compare to the 2009 TT4 results. The fractional polynomial regression was:

TT4 (modified) = 4.067036 + 5.492497*((TT4/10.0)**3) - 5.673583*((TT4/10.0)**3)*log(TT4/10.0)

Researchers may want to use this regression equation to trend 2011-2012 TT4 data with TT4 data of previous NHANES cycles.

NHANES survey analysis:

Refer to the 2011-2012 Laboratory Data Overview for general information on NHANES laboratory data.

The analysis of NHANES 2011-2012 laboratory data must be conducted using the appropriate survey design and demographic variables. The NHANES 2011-2012 Demographics File contains demographic data, health indicators, and other related information collected during household interviews as well as the sample weight variables. The Fasting Questionnaire File includes auxiliary information such as fasting status, the time of venipuncture, and the conditions precluding venipuncture. The demographics and fasting questionnaire files may be linked to the laboratory data file using the unique survey participant identifier (i.e., SEQN).

Subsample Weights

Measures of thyroid profile were assessed in a one third subsample of participants aged 12 years and older. Special sample weights are required to analyze these data properly. Specific sample weights for this subsample are included in this data file and should be used when analyzing these data.

Variance Estimation

The analysis of NHANES laboratory data must be conducted with the key survey design and basic demographic variables. The NHANES Demographic Data File contains demographic and 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.

Links to NHANES Data Files

This laboratory data file can be linked to the other NHANES data files using the unique survey participant identifier SEQN.

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