Background: Treatment of congenital primary hypothyroidism (CPHT) fluctuates between two opposite risks for the neuro-cognitive development in a critical window during the neonatal period, under- and over-treatment.
Objective: To investigate the relevance of current international recommendations of 1015 μg/kg per day for L-thyroxine (lT4) doses in CPHT.
Method: fT4 and TSH were measured in a plasma sample after 15 days and one month of lT4 treatment in 90 healthy full term newborns diagnosed with congenital hypothyroidism from routine screening on the 3rd day of life over a period of 9 years 3 months who were treated with doses of a liquid preparation of lT4, ranging from 6.3 (2.5th percentile) to 11.6 (97.5th percentile) (median: 8.0) μg/kg per day. fT4 and TSH levels at the 15th day of treatment served to adjust lT4 doses.
Results: At the 15th day of treatment, only 4.8% of the newborns had a plasma fT4 level below the lower value of 12 pmoles/l, while 46.7% and 32.2% had a plasma fT4 level above the upper values of 25 or 30 pmoles/l respectively. A significant independent positive correlation (r2=0.2, P=0.0027) was observed between fT4 plasma levels at the 15th day of life and the initial lT4 dose. The relationship between 15 day lT4 dose and fT4 at 1 month of treatment was weaker.
Conclusions: Although significant enough, the correlation between initial lT4 doses and fT4 level at the 15th day is characterised by a dispersion inducing a frequent overtreatment by liquid lT4 administration, when following recommended 1015 μg/kg per day dosages in newborns with CPHT, whose neuro-cognitive consequences are to evaluate.
Funding: French National Insurance Organization (Fund for Neonatal Screening).
01 - 03 Oct 2015
European Society for Paediatric Endocrinology