Cited by 281Thyroid Disorders and TreatmentsClinical Laboratory Practices and Quality ControlThyroid Cancer Diagnosis and Treatment

Free T4 immunoassays are flawed during pregnancy

Lee, Richard H., Spencer, Carole A., Mestman, Jorge H., Miller, Erin A., Petrovic, Ivana, Braverman, Lewis E., Goodwin, T. Murphy·2009·American Journal of Obstetrics and Gynecology

Abstract

Objective The purpose of this study was to evaluate the diagnostic accuracies of 2 free thyroxine immunoassays during pregnancy.Study design Serum was collected from healthy, thyroid peroxidase antibody-negative women during each trimester and nonpregnant controls. Thyrotropin, total T4 (TT4), free T4 index (FT4I), and 2 different FT4 immunoassays were studied.Results As expected, TT4 was elevated in all 3 trimesters compared to controls (P < .001). FT4I was elevated in the 1st trimester as compared with controls (P < .05) and returned to the nonpregnant range in the 2nd and 3rd trimesters. In contrast, 1st trimester FT4 immunoassay values were either comparable or lower than controls and by the 2nd and 3rd trimesters had decreased to approximately 65% of controls.Conclusion Neither FT4 immunoassay accurately reflects established free T4 changes during pregnancy. TT4 and the FT4I retained an appropriate inverse relationship with TSH throughout pregnancy and appear to provide a more reliable free T4 estimate.

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Crossref · 10.1016/j.ajog.2008.10.042

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Authors
Lee, R. H., Spencer, C. A., Mestman, J. H., Miller, E. A., Petrovic, I., Braverman, L. E., & Goodwin, T. M.
Affiliations
  • University of Southern California (US)
  • Boston University (US)
Venue
American Journal of Obstetrics and Gynecology
Publisher
Elsevier BV
Published
2009-03
Volume
200
Issue
3
Pages
260.e1-260.e6
ISSN
0002-9378 (ISSN-L)
OpenAlex
W2011956011
Cited by
281
References
17
Citations by year
2026: 3 · 2025: 6 · 2024: 7 · 2023: 9 · 2022: 22 · 2021: 9 · 2020: 13 · 2019: 18 · 2018: 20 · 2017: 18 · 2016: 18 · 2015: 17 · 2014: 19 · 2013: 26 · 2012: 22
FWCI
12.48
Type
journal article
Language
en
Open access
closed
Locations
  • American Journal of Obstetrics and Gynecology (publishedVersion)
  • PubMed (publishedVersion)
Topics
  • Health Sciences › Medicine › Endocrinology, Diabetes and Metabolism › Thyroid Disorders and Treatments
  • Health Sciences › Medicine › Physiology › Clinical Laboratory Practices and Quality Control
  • Health Sciences › Medicine › Endocrinology, Diabetes and Metabolism › Thyroid Cancer Diagnosis and Treatment
Keywords
free thyroxine, pregnancy, free T4 index, total thyroxine, thyroid-stimulating hormone, thyroid function in pregnancy, diagnostic accuracy, pregnancy trimesters
MeSH terms
Chemistry, Clinical, Female, Humans, Immunoassay, Pregnancy, Reference Values, Thyroid Gland, Thyrotropin, Thyroxine, Reproducibility of Results

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