Newborn screening TSH values <15 mIU/L are not associated with long-term hypothyroidism or cognitive impairment

BACKGROUND It is unclear whether newborns with mild TSH elevation (mTSHe) are at risk of neurocognitive impairment. We assessed whether mTSHe at birth persists during childhood and compared neurocognitive functioning to siblings. METHODS This study encompassed children born in the Auckland region with a newborn screen TSH level 8-14 mIU/L blood, aged 6.9-12.6 years at assessment, and their siblings. Thyroid function tests (serum TSH and FT4) and neurocognitive assessments were performed, including intelligent quotient (IQ) via Wechsler Intelligence Scale for Children IV. RESULTS Ninety-six mTSHe subjects were studied, including 67 children recruited with 75 sibling controls. Mean mTSHe newborn TSH level was 10.1 mIU/L (range 8-14 mIU/L, blood) and 2.4 mIU/L at assessment (range 0.8-7.0 mIU/L, serum). Although higher newborn TSH levels in the mTSHe group correlated with lower full-scale IQ scores (r=0.25; p=0.040), they were not associated with the magnitude of the IQ difference within sibling pairs (p=0.56). Cognitive scores were similar for mTSHe and controls (full-scale IQ 107 vs 109; p=0.36), with a minor isolated difference in motor co-ordination scores. CONCLUSIONS Our data do not demonstrate long-term negative effects of neonatal mild TSH elevation. TSH elevation below screen threshold appears largely transient and mid-childhood neurocognitive performance of these children was similar to their siblings. We propose that associations between neonatal mild TSH elevation and IQ are due to familial confounders. We caution against the practice of reducing screening CH cutoffs to levels where the diagnosis may not offer long-term benefit for those detected.