The Impact of Seasonal Changes on Thyroxine and Thyroid-Stimulating Hormone in Newborns

Rebecca Mcmahon,Mycroft Sowizral,Melissa Tracy,Diana Powers,Michele Caggana,Lenore Demartino,Norma P Tavakoli

doi:10.3390/ijns7010008

Abstract

Newborn screening for congenital hypothyroidism (CH) is performed by measuring the concentration of thyroxine (T4) and/or thyroid-stimulating hormone (TSH) in dried blood spots. Unfortunately, the levels of T4 and TSH vary due to multiple factors, and therefore the false-positive rate for the test is a challenge. We analyzed screening data from 2008 to 2017 to determine the effect of seasonal changes and manufacturer kit lot changes on T4 and TSH values and on numbers of infants referred. Over a 10-year period, we screened 2.4 million infants using commercially available fluoroimmunoassays to measure T4 and TSH concentrations in dried blood spots. During colder months, daily mean T4 and TSH values were higher and referral rates and false-positive rates were higher. However, there was no significant difference between the number of confirmed CH cases. Furthermore, in rare instances, we observed differences in T4 daily mean values during the 10-year period when manufacturer kit lot changes were made. Seasonal temperature variations influence measured T4 and TSH values and consequently lower the positive predictive value for CH testing in colder months. Newborn screening (NBS) programs should be aware that manufacturer kit lot changes may also influence T4 values.

Highlights

Newborn screening (NBS) for congenital hypothyroidism (CH) is performed routinely in most of the developed world, where it has led to the near elimination of intellectual disability caused by this common condition
NBS for CH is complicated because T4 and thyroid-stimulating hormone (TSH) values are affected by factors including prematurity, birth weight, and age at specimen collection [3,5,15]
Differences in T4 and TSH values in male and female infants lead to a higher number of false-positive cases amongst male infants [16]

Summary

Introduction

Newborn screening (NBS) for congenital hypothyroidism (CH) is performed routinely in most of the developed world, where it has led to the near elimination of intellectual disability caused by this common condition. There has been a dramatic increase in the survival of very LBW babies, who in addition to having low T4 at birth have a higher incidence of transient hypothyroidism than full-term infants [11]. These factors lead to frequent false-positive CH results, especially when specimens are collected too soon after birth and in premature or LBW infants. Many NBS programs have higher cut-offs for TSH when the specimen is collected within the first 24 h after birth. Age-related cut-offs have been recommended [12,13]

Methods

Results

Conclusion