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

BACKGROUND: 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. METHODS: 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). RESULTS: 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). CONCLUSION: 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.

IFCC international conventional reference procedure for the measurement of free thyroxine in serum: International Federation of Clinical Chemistry and Laboratory Medicine (IFCC) Working Group for Standardization of Thyroid Function Tests (WG-STFT)(1).

The IFCC Working Group for Standardization of Thyroid Function Tests proposes a candidate international conventional reference procedure (RMP) for measurement of the amount-of-substance concentration of free thyroxine in plasma/serum at physiological pH 7.40 and temperature (37.0°C). The unit for reporting measurement results is, by convention, pmol/L. The RMP is based on equilibrium dialysis isotope dilution-liquid chromatography/tandem mass spectrometry (ED-ID-LC/tandem MS). The rationale for proposing a conventional RMP is that, because of the physical separation step, it is unknown whether the measurement truly reflects the concentration of free thyroxine (FT4) in serum. Therefore, the ED part of the RMP has to strictly adhere to the following conditions: use of a dialysis buffer with a biochemical composition resembling the ionic environment of serum/plasma as closely as possible; buffering of the sample to a pH of 7.40 (at 37.0°C) before dialysis, however, without additional dilution; dialysis in a device with a dialysand/dialysate compartment of identical volume and separated by a membrane of regenerated cellulose and adequate cut-off; thermostatic control of the temperature during dialysis at 37.0°C±0.50°C. The convention does not apply to the ID-LC/tandem MS part, provided it is eligible to be nominated for review by the Joint Committee for Traceability in Laboratory Medicine. Here, we describe the ED procedure, inclusive its validation and transferability, in greater detail. We recommend a protocol for successful calibration, measurement and monitoring of the accuracy/trueness and precision of the candidate conventional RMP. For details on our ID-LC/tandem MS procedures, we refer to the Supplement.

The medical treatment of non-toxic goiter: several questions remain.

In this review it is concluded that thyroxine (T4), triiodothyronine (T3) and iodine (KI), singly or in combination, are all effective in reducing the goiter size, but there is insufficient evidence to prove which is the best (possibly the combination of T4 + KI?). Higher doses are more effective than smaller, but also lead to more side-effects. Thus, the optimal dose has yet to be found. The suppression of the pituitary thyroid axis plays a major role in the treatment of non-toxic goiter, but it is not definite that this is the only mechanism responsible for the beneficial effect of the agents mentioned. In view of the lack of better evidence, it is simply suggested that non-toxic goiters in young persons should be initially treated aggressively with 200 micrograms of T4/day or more for some months. If the goiter shrinks then the dose should be gradually decreased. If the goiter persists, it is futile to continue with large doses for more than 6-12 months. One may continue with smaller doses, maintaining the serum TSH in the low-normal range. The treatment of benign thyroid nodules with thyroxine is controversial. Probably thyroxine is beneficial in about a third of the cases. For both non-toxic goiters and nodules, autonomy should be excluded before starting thyroxine treatment, and old age, cardiac disease and a poor general condition are contraindications.