Reference intervals for preterm thyroid function during the fifth to seventh day of life.

Due to the lack of reference intervals for serum free triiodothyronine (FT3), free thyroxine (FT4) and thyroid stimulating hormone (TSH) in preterm neonates during the 5th to 7th day of life, we performed a retrospective study using the chemiluminescence immunoassay system. A total of 2040 preterm neonates with a gestational age (GA) of 26-35 weeks in the neonatal intensive care unit from 2014 to 2019 were included. Their serum FT3, FT4 and TSH values were calculated and analyzed to establish reference intervals for preterm neonates stratified by GA. The comparisons of FT3, FT4 and TSH were made by sex (males and females) and gestational age (26-28 weeks; 29-32 weeks; 33-35 weeks). The reference intervals for FT3, FT4 and TSH in preterm neonates with a GA of 26-35 weeks were (1.65~5.21) pmol/L, (8.64~25.41) pmol/L, and (0.406~12.468) mlU/L, respectively. There were significant differences between serum FT3 and FT4 values and GA, while TSH levels were not significantly different (P < 0.01). The serum FT3 values of males were lower than those of females, especially in the 29-32 weeks group. No significant differences in serum values between sexes were found in FT4 or TSH (P > 0.05). Reference intervals of thyroid function tests were established to determine the early diagnostic criteria of thyroid diseases for neonates with a GA of 26-35 weeks and to avoid unnecessary retesting and interventions. The reference intervals of FT4 can be used as an indicator to regulate the doses of thyroid hormone supplement in the treatments of congenital hypothyroidism.

Lin X ，Zheng LJ ，Li HB ，Yang CY ... -  《-》

Reference intervals for thyroid function from the fifth to seventh day of life in twin-pregnancy preterm neonates: an 8-year retrospective study.

The immature and developing hypothalamic-pituitary-thyroid axis leads to different levels of thyroid function in twin neonates, including free thyroxine (FT4), free triiodothyronine (FT3), and thyroid stimulating hormone (TSH) levels. No reference intervals for twins have been established until now. To compensate for this lack, we collected data and established this standard across different gestational ages (GAs) and sexes. A total of 273 pairs of neonates admitted to the NICU in Southeast China from 2015 to 2022 were included. Each pair was divided into Neonate A (relatively heavy birth weight (BW)) and Neonate B (relatively light BW). Their thyroid functions were analyzed to establish reference intervals and comparisons were made stratified by GA and sex. The FT3, FT4, and TSH reference intervals in twin neonates with a GA of 26-36 weeks were as follows: Neonate A and B: 3.59 ± 0.99 and 3.57 ± 1.00 pmol/L; Neonate A and B: 17.03 ± 5.16 and 16.77 ± 5.29 pmol/L; and Neonate A and B: 4.097 ± 3.688 and 4.674 ± 4.850 mlU/L, respectively. There were significant differences between serum FT3 and FT4 reference intervals and GA (p < 0.05). The serum FT3 and FT4 reference intervals for male neonates were lower than those for female neonates in the 29-32-week group (p < 0.05). This was the first study, to our knowledge, to establish reference intervals for thyroid function in twin neonates from the fifth to seventh day of life, which will be beneficial for the diagnosis and management of congenital hypothyroidism.

Zheng XT ，Lin X ，Ma M ，Lai SH ，Yang CY ... -  《-》

Reference intervals for thyroid-stimulating hormone, free thyroxine, and free triiodothyronine in elderly Chinese persons.

Wang D ，Yu S ，Ma C ，Li H ，Qiu L ，Cheng X ，Guo X ，Yin Y ，Li D ，Wang Z ，Hu Y ，Lu S ，Yang G ，Liu H ... -  《-》

Establishment of reference intervals for thyroid hormones in premature infants beyond the first week of life using Beckman Coulter Unicel DxI 800.

This 4-year retrospective cohort study aimed to establish reference intervals for free triiodothyronine (FT3), free thyroxine (FT4), and thyrotropin (TSH) in premature infants using the Beckman Coulter Unicel DxI 800 automated immunoassay system. Study subjects included 605 preterm infants with a gestational age of 26-36 weeks (corrected: 29-38 weeks). Pearson correlation was used to evaluate the association between hormone levels and gestational and corrected gestational ages. A nonparametric method was used to establish reference intervals based on corrected gestational age. FT3 and FT4 levels were positively correlated with gestational and corrected gestational ages, respectively. TSH levels were slightly negatively correlated with gestational and corrected gestational ages. FT3 significantly differed according to corrected gestational age (29-33 weeks vs 34-38 weeks); however, the difference was smaller than the reference change value (RCV) for the FT3 test. Thus, we combined the FT3 reference intervals into a single reference interval: 2.65-4.93 pmol/L (29-38 weeks). The reference intervals of FT4 and TSH were 11.20-24.97 pmol/L (29-38 weeks) and 1.01-10.14 mIU/L (29-38 weeks), respectively. Unlike those of full-term infants or adults, the reference intervals established in this study are applicable in premature infants. These results highlight the importance and complexity of establishing instrument-specific thyroid hormone reference intervals for preterm infants.

Wang Y ，Wu X ，Hong K ，Fu X ，Chen T ，Zhu M ，Ye H ... -  《-》

Reference intervals for thyroid-stimulating hormone (TSH) and free thyroxine (FT4) in infants' day 14-30 of life and a comparison with other studies.

Wong JSL ，Selveindran NM ，Mohamed RZ ，Zain FM ，Anas SS ，Hong JYH ... -  《-》