First- and Second-Trimester Reference Intervals for Thyroid Function Testing in a US Population.

OBJECTIVES Thyroid dysfunction in pregnancy is associated with increased risk of adverse outcomes to mother and child. Trimester-specific reference intervals for thyroid function tests are not routinely provided by clinical laboratories. In this study, we present first- and second-trimester-specific reference intervals in a US population for thyroid-stimulating hormone (TSH), free thyroxine (FT4), total thyroxine (T4), and total triiodothyronine (T3) measured on Roche analyzers. METHODS We used patient samples from first- and second-trimester prenatal screening. Samples were limited to singleton pregnancies and negative screening results for thyroid peroxidase and thyroglobulin antibodies. Analytes (TSH, FT4, T4, and T3) were measured on a Roche Modular e170 then verified on a Roche cobas e801. RESULTS The reference intervals established on the e170 and verified on the e801 for the first trimester were 0.11 to 3.48 mIU/L for TSH, 11.2 to 19.0 pmol/L for FT4, 51.1 to 185.6 nmol/L for T4, and 1.4 to 3.5 nmol/L for T3. The reference intervals for the second trimester were 0.31 to 3.85 mIU/L for TSH, 9.4 to 16.5 pmol/L for FT4, 55.1 to 174.0 nmol/L for T4, and 1.5 to 3.7 nmol/L for T3. CONCLUSIONS This is the first report of trimester-specific reference intervals for thyroid function tests on Roche analyzers in the United States, and it is consistent with worldwide reports.