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First trimester of pregnancy TSH laboratory specific reference intervals established by an indirect method
María Sanz-Felisi1, Ariadna Arbiol-Roca1, Paula Sánchez-García2
1Clinical Laboratory, Bellvitge University Hospital, L'Hospitalet de Llobregat, Barcelona, Spain.
Introduction:
This study established laboratory and trimester specific indirect reference intervals (RIs) for thyroid stimulating hormone (TSH).
Materials And Methods:
A retrospective observational study was performed at a tertiary-care laboratory's hospital during 12 months. Between February 2023 and February 2024, TSH results from 2166 women in their first trimester of pregnancy were retrieved. Only outpatients coming from primary care were included in the study. After applying exclusion and outlier criteria, TSH results from 1300 patients were analyzed to establish new RIs using the 2.5th and 97.5th percentiles by the non-parametric percentile method. These RIs were verified by an indirect method analyzing 486 TSH results from a cohort of pregnant women that were extracted from April to June 2024, and a direct prospective study of 28 pregnant women from a primary care center. All TSH tests were measured using a Cobas 8000 e801 system (Roche, Basel, Switzerland).
Results:
The TSH RIs were 0.60-4.33 mIU/L. Both verification methods met the requirements of the CLSI guidelines.
Conclusions:
The indirect method could be used to establish and verify local RIs for TSH in first trimester pregnant women. This may reduce misclassification of pregnant women undergoing thyroid function tests.
