Clinical Evaluation of Nine Free Thyroxine Assays: Persistent Problems in Particular Populations

d’Herbomez, Michèle; Forzy, G.; Gasser, F; Massart, Catherine; Beaudonnet, A; Sapin, R

doi:10.1515/cclm.2003.143

Cited by 71 publications

(50 citation statements)

References 23 publications

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“…"Outlier values" were specifically not excluded from any of the analyses because of the previously documented substantial disagreement between values obtained by different assays (28)(29)(30)33). The relationship between FT 4 and TSH was investigated using log-transformed TSH values.…”

Section: Discussionmentioning

confidence: 99%

“…Not only are gestation-related changes in binding proteins such as thyroxine-binding globulin and albumin substantial, but also each immunoassay used to measure FT 4 is affected to a varying and unpredictable degree by protein binding (27)(28)(29)(30). Therefore, different FT 4 assays may produce discrepant results (9,(27)(28)(29)(31)(32)(33). Thus, pregnancy reference intervals ideally should not only be trimester specific, but also method specific (9).…”

Section: Introductionmentioning

confidence: 99%

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Tandem Mass Spectrometry Improves the Accuracy of Free Thyroxine Measurements During Pregnancy

Kahric-Janicic

Soldin

et al. 2007

Thyroid

145

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Objective-Pregnancy is a time of rapidly changing demands on the thyroid axis, and knowledge of thyroid hormone levels, especially during the first trimester, is important for ensuring maternal and fetal health. The thyroid hormone assays currently in use become more inaccurate at extremes of binding protein concentrations and when heterophilic antibodies are present. Pregnancy is characterized by both these conditions, making accurate determination of free thyroid hormone levels by conventional direct analog immunoassay methods difficult. The objective of this study was to characterize the performance of a novel tandem mass spectrometric assay for free thyroxine during the physiologic conditions of pregnancy.Design-Healthy women without a history of thyroid abnormalities were recruited from the obstetrics and gynecology and endocrinology clinics of a university medical center and their thyroid status was monitored. Free thyroxine levels were assessed by both immunoassay and tandem mass spectrometry during the course of their pregnancy. Serum thyrotropin levels were also measured. The distributions of free thyroid concentrations obtained by the two assays were compared.Main outcome-The tandem mass spectrometry and immunoassay values did not correlate well with each other. However, tandem mass spectrometry values correlated well with the current gold standard equilibrium dialysis values. Moreover, the good agreement between equilibrium dialysis and tandem mass spectrometry was maintained across all weeks of gestation.Conclusions-We conclude that tandem mass spectrometry has a superior performance to immunoassay for the measurement of free thyroxine during pregnancy. Furthermore, it is ideally suited to generating trimester-specific reference intervals for free thyroxine levels. Future studies will determine if it is a better assay to use in most clinical circumstances.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Tandem Mass Spectrometry Improves the Accuracy of Free Thyroxine Measurements During Pregnancy

Kahric-Janicic

Soldin

et al. 2007

Thyroid

145

View full text Add to dashboard Cite

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“…The overall performance of the fT 4 assay has generally been good (22). Both accuracy and reliability of the assay have been ascertained by participation in inter-laboratory tests throughout the study period.…”

Section: Value ((Xka)mentioning

confidence: 99%

“…The possibility of a potential bias in fT 4 immunoassays should be mentioned, but has been observed, almost exclusively, in specific populations such as pregnant women, patients with renal failure or severely ill patients that had been excluded (19)(20)(21)(22). The overall performance of the fT 4 assay has generally been good (22).…”

Section: Value ((Xka)mentioning

confidence: 99%

Complex relationship between free thyroxine and TSH in the regulation of thyroid function

Hoermann

Eckl²,

Hoermann³

et al. 2010

European Journal of Endocrinology

100

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Objective: The present study re-evaluates the inverse log TSH-free thyroxine (fT 4 ) relationship, which has generally been assumed to characterize the thyroid pituitary hypothalamic feedback regulation in thyroid function. Design and Methods: The correlation between fT 4 and TSH was analyzed in two data sets from differing time periods involving 3223 and 6605 patients referred for thyroid testing, representing the whole range of thyroid functions from hypothyroidism to hyperthyroidism. Results: We found that the data do not support a linear log TSH-fT 4 relationship; instead, the correlation's gradient varies with thyroid function. As a consequence, an alternate model, based on the error function, was introduced. When directly comparing the models by means of curve fitting, using F-test and Akaike criteria, the alternate model results in a significantly better fit. The model was verified in the independent second set of data. Subgroup analysis of untreated patients added further proof to the non-linear model. Conclusions: We propose a refined non-linear model to describe the relationship between TSH and fT 4 . It implies that TSH response to a deviating fT 4 value may not be log-linear, but may be disproportionally related to the extent of the deviation from an optimum set point. A better understanding of the complex nature of the TSH-fT 4 relationship may further the development of more precise clinical models and aid in better defining subclinical states of thyroid dysfunction. Also, it may encourage other biological interrelations to be reconsidered in the wake of advanced measurement techniques and more powerful computerized statistical procedures.

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“…Although previous studies have shown that the interassay differences for TSH are relatively small (r ϭ 0.91-0.98), FT 4 measurements seem much more prone to interference and have larger interassay differences (r ϭ 0.68 -0.89) (33,34 ). Pregnancy results in a shift of potentially interfering factors such as thyroxinebinding globulin and albumin.…”

Section: Factors Influencing Thyroid Function Reference Intervals Durmentioning

confidence: 99%

Thyroid Function in Pregnancy: What Is Normal?

Medici¹,

Korevaar²,

Visser³

et al. 2015

Clinical Chemistry

168

110

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BACKGROUND:Gestational thyroid dysfunction is common and associated with maternal and child morbidity and mortality. During pregnancy, profound changes in thyroid physiology occur, resulting in different thyroidstimulating hormone (TSH) and free thyroxine (FT 4 ) reference intervals compared to the nonpregnant state. Therefore, international guidelines recommend calculating trimester-and assay-specific reference intervals per center. If these reference intervals are unavailable, TSH reference intervals of 0.1-2.5 mU/L for the first trimester and 0.2-3.0 mU/L for the second trimester are recommended. In daily practice, most institutions do not calculate institution-specific reference intervals but rely on these fixed reference intervals for the diagnosis and treatment of thyroid disorders during pregnancy. However, the calculated reference intervals for several additional pregnancy cohorts have been published in the last few years and show substantial variation. CONTENT:We provide a detailed overview of the available studies on thyroid function reference intervals during pregnancy, different factors that contribute to these reference intervals, and the maternal and child complications associated with only minor variations in thyroid function.

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Clinical Evaluation of Nine Free Thyroxine Assays: Persistent Problems in Particular Populations

Cited by 71 publications

References 23 publications

Tandem Mass Spectrometry Improves the Accuracy of Free Thyroxine Measurements During Pregnancy

Tandem Mass Spectrometry Improves the Accuracy of Free Thyroxine Measurements During Pregnancy

Complex relationship between free thyroxine and TSH in the regulation of thyroid function

Thyroid Function in Pregnancy: What Is Normal?

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