Indexed on: 06 Aug '16Published on: 06 Aug '16Published in: Pediatric Research
In congenital hypothyroidism (CH) age-specific reference ranges for fT4 and TSH (asRR) are usually used to signal over/under-treatment. We compared the consequences of individual fT4 steady state concentrations (SSC's) and asRR regarding over-treatment signalling and intelligence quotient at 11 years (IQ11) and the effect of early over-treatment with high L-T4 dosages on IQ11.61 patients (27 severe, 34 mild CH) were psychologically tested at 1.8, 6, and 11 years. Development scores were related to over-treatment in period 0-24m, relative to either individual fT4SSC's or asRR. Three groups were formed, based on severity of over/under-treatment 0-5m (Severe, Mild, and No over/under-treatment).FT4 and TSH asRR missed 41-50% of the over-treatment episodes and consequently 22% of the over-treated patients, classified as such by fT4 SSC's. Severe over-treatment 0-5m led to lowered IQ11's and to a 5.5 fold higher risk of IQ11<85 than other treatment regimes. Under-treatment had no effect on development scores. Initial L-T4 dosages >10 µg/kg resulted in a 3.7 fold higher risk of over-treatment than lower dosages.Data suggest that asRR, compared to fT4 SSC's, signal over-treatment insufficiently. Using fT4 SSC's and avoiding over-treatment may optimize cognitive outcome.Lowered IQ11's are usually a late complication of severe early over-treatment.