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Method-dependent variation in TSH and FT4 reference intervals in pregnancy: A systematic review
Onyebuchi E Okosieme1,2, Medha Agrawal1,2, Danyal Usman1,2
1Thyroid Research Group, School of Medicine, Cardiff University, Cardiff, UK.
Annals of Clinical Biochemistry
|June 14, 2021
Summary
Thyroid stimulating hormone (TSH) and free thyroxine (FT4) reference intervals in pregnancy vary significantly by assay method. These variations highlight the need for method-specific gestational reference intervals, not extrapolation from non-pregnant values.
Area of Science:
- Endocrinology
- Clinical Chemistry
- Reproductive Medicine
Background:
- Thyroid stimulating hormone (TSH) and free thyroxine (FT4) reference intervals during pregnancy are crucial for diagnosing thyroid dysfunction.
- Existing reference intervals may differ based on assay methods, but systematic evaluations are lacking.
Purpose of the Study:
- To systematically review and quantify method-related differences in gestational TSH and FT4 reference intervals.
- To compare intervals across four common assay methods: Abbott, Beckman, Roche, and Siemens.
Main Methods:
- Systematic literature search for studies published between 2000 and 2020.
- Inclusion of studies on healthy pregnant women without thyroid antibodies or disease.
- Extraction of trimester-specific TSH and FT4 reference intervals (2.5-97.5 percentiles) and non-pregnant reference intervals.
Main Results:
- Significant study-to-study variation in TSH and FT4 reference intervals was observed.
- The Beckman method consistently showed lower FT4 reference intervals.
- First-trimester TSH upper limits were highly variable and often unpredictable from non-pregnant values.
Conclusions:
- Significant intra- and inter-method disparities exist in gestational thyroid hormone reference intervals.
- Extrapolating non-pregnant values for gestational references is unreliable.
- Laboratories should establish method-specific gestational reference intervals for their populations.
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