Background: Subclinical hypothyroidism (SH) is defined as normal tyrosine levels in the presence of TSH concentrations between 5 and 10 mU/ml. The impact of SH on IGF system and growth of infants remains unknown.
Objective and hypotheses: To evaluate IGF1, IGFBP3 levels and growth velocity (GV) of infants with SH.
Method: 98 children up to 36 months of age, recalled due to a TSH >5 mU/ml in the neonatal screening test, were divided in two age-groups: I (04 months) and II (4.136 months). They were further split into subgroups according to the TSH level observed during follow-up: IA (n=14) and IIA (n=49), TSH ≤5 mU/ml, IB (n=5) and IIB (n=16), 5<TSH ≤10 mU/ml and IC (n=4) and IIC (n=10), TSH >10 mU/ml. GV-SDS was calculated based on the previous 3 months of follow-up. IGF1 and IGFBP3 were determined by Immulite 2000 Kits in the same blood sample as TSH.
Results: No difference was observed between group IA, IB, and IC regarding IGF1, IGFBP3 levels or GV, even when group IA was compared to combined IB+IC. However, IGF1 levels were higher in IIA than in IIB and IIC (median: 66, 36, and 30 ng/ml, respectively, P=0.005). Similar results were observed for GV-SDS (mean±S.E.M.) with higher values in IIA (0.74±0.3) than in IIB (−0.78±0.4) and IIC (−0.5±0.5)(P=0.03). These findings were even more significant when IIA was compared to IIB+IIC (IGF1: 38 ng/ml, P=0.001; GV: −0.67±0.3, P=0.004). No difference was found on IGFBP3 levels. Negative correlation was observed between TSH and IGF1 levels (r=0.32, P=0.005).
Conclusion: Reduced serum IGF1 levels and GV were observed in children aged 436 months with SH. This was not found earlier in life. These findings may reflect a direct action of thyroid hormones on IGF1 secretion rather than a modulation of GH action, as no changes were found on IGFBP3 levels. The real impact on height would demand a longer period of observation.
20 - 22 Sep 2014
European Society for Paediatric Endocrinology