National Health and Nutrition Examination Survey

2001-2002 Data Documentation, Codebook, and Frequencies

Transferrin Receptor - Pregnant Women (Surplus) (SSTFR_B)

Data File: SSTFR_B.xpt

First Published: July 2008

Last Revised: April 2022

Note: The NHANES Biospecimen Program processes were reevaluated in 2021 and 2022 to monitor quality control after a procedural error was identified. This error did not pose any risk of participant disclosure. Addressing this error resulted in the removal of some records from various stored biospecimen data files between 1999 and 2018 that did not meet program standards. After a comprehensive review of all stored specimen datasets, this data file was modified to remove records (5-<10% of records) that were initially included in error. No data values were altered. The sample weights and overall estimates were compared between the original and revised files. The sample weights provided with the original data release are appropriate to use with this updated data file; therefore, no new survey weights were created. The overall estimates from these files were examined and are consistent with the previous file. However, not all possible analyses were performed. For any queries related to this dataset please email the Biospecimen Program at serumplasmaurine@cdc.gov.

Component Description

Serum transferrin receptor and ferritin were measured in pregnant women from NHANES 2001-2002 to provide estimates of iron deficiency based on body iron levels observed in these women. Body iron estimates can be predicted using an equation that includes measured serum transferrin receptor and serum ferritin levels. Serum transferrin receptor was not added to NHANES until 2003. Serum ferritin was measured in NHANES 2001-2002 with a method that has now been shown to differ from the method needed to provide the appropriate ferritin values for use in the body iron model equation. Thus, serum ferritin was re-measured using the appropriate method for body iron calculations.

Eligible Sample

Pregnant women aged 13 to 56 years from NHANES 2001-2002 with stored sera (N = 625). The pregnant women for this sample were identified using either one of the two available summary pregnancy variables (RIDEXPRG or RIDPREG) or in the case of 20 women < 18 years of age from NHANES 1999-2000, with the self-reported pregnancy item RHQ140. This item was used for these 20 women because RIDEXPRG and RIDPREG were not provided for women < 18 years of age in NHANES 1999-2000.

Description of Laboratory Methodology

The method for measurement of soluble transferrin receptor (sTfR) is immuno-turbidimetry using Roche kits on the Hitachi 912 clinical analyzer. Latex bound anti-sTfR antibodies react with the antigen in the sample to form an antigen/antibody complex. Following agglutination, this is measured turbidimetrically. This is the same method used to measures sTfR starting in NHANES 2003+.

The method principle for measurement of Ferritin is immuno-turbidimetry using the Roche/Hitachi 912 clinical analyzer. Latex bound Ferritin antibodies react with the antigen in the sample to form an antigen/antibody complex. Following agglutination, this is measured turbidimetrically. Complexes formed are proportional to the Ferritin concentration, and were measured at 700nm (primary wavelength). This is the same method used to measure serum ferritin starting in NHANES 2004. These ferritin data do not need to be adjusted to be compared with NHANES 2003-2004 ferritin data.

Data Processing and Editing

Data was received after the sTfR and ferritin assays were complete. The data were not edited.

Data Access: All data are publicly available.

Laboratory Quality Assurance and Monitoring

The NHANES quality control and quality assurance protocols (QA/QC) meet the 1988 Clinical Laboratory Improvement Amendments mandates. Detailed quality control and quality assurance instructions are discussed in the NHANES Laboratory/Medical Technologists Procedures Manual (LPM). A detailed description of the quality assurance and quality control procedures can be found at NHANES web site.

Analytic Notes

There are two variables:

LBXTFR: serum transferrin receptor (mg/L)
LBXFER: Serum ferritin (ng/mL)

Codebook and Frequencies

SEQN - Respondent sequence number

Variable Name:: SEQN
SAS Label:: Respondent sequence number
English Text:: Respondent sequence number.
Target:: Females only 13 YEARS - 56 YEARS

SSTFR - Serum transferrin receptor (mg/l)

Variable Name:: SSTFR
SAS Label:: Serum transferrin receptor (mg/l)
English Text:: Serum transferrin receptor (mg/l)
Target:: Females only 13 YEARS - 56 YEARS

Code or Value	Value Description	Count	Cumulative	Skip to Item
1.5 to 18	Range of Values	322	322
.	Missing	0	322

SSFER - Serum ferritin (ng/ml)

Variable Name:: SSFER
SAS Label:: Serum ferritin (ng/ml)
English Text:: Serum ferritin (ng/ml)
Target:: Females only 13 YEARS - 56 YEARS

Code or Value	Value Description	Count	Cumulative	Skip to Item
3 to 394	Range of Values	322	322
.	Missing	0	322

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