ESPE Abstracts

Background: Up to 20% of infants referred on newborn congenital hypothyroidism (CH) screening are subsequently shown to have transient TSH elevation rather than permanent CH. Correct identification of such cases is important to avoid prolonged treatment with thyroxine and unnecessary clinic attendance.

Objective: To determine the prevalence, trends and profile of infants with transient TSH elevation referred between August 1979 and December 2015 by the Scottish Newborn Programme.

Method: Analysis of infants referred during the study period with initial/repeat capillary TSH ≥50/≥25 mU/l (1979–82); ≥40/≥15 (1982–89); ≥40/≥10 (1989–2002); ≥25/≥8 (2002–15) in whom venous thyroid function tests became normal off thyroxine. Details of gestation, birthweight (BW), “sickness” and extra-thyroidal congenital malformations (CM) were recorded.

Results: Of 2,202,191 newborns screened, 936 were referred by the screening laboratory including 630 (68.9%) with definite CH; and 208 (22.8%) with transient TSH elevation. The transient group differed from the true CH group in terms of mean BW (2.68 vs 3.34 kg), BW <2500 g (30.3 vs 9.2%) gestation (36.5 vs 39.6 weeks), gestation <30 weeks (12.9 vs 0.5%), “sickness” (35.6 vs 7.1%), and presence of CM (20.7 vs 5.7%). Median capillary TSH (37.0 vs 167.5 mU/l), need for 2^nd capillary sample (50 vs 12%), mean initial venous fT4 (15.15 vs 6.6 pmol/l) and TSH (12.5 vs 102 mU/l) were all significantly different (P=<0.001). Specific aetiology in the 208 transient infants was found in a minority only and included blocking maternal antibodies (3), maternal carbimazole (1), Pendrin (1) and TSH receptor heterozygosity (1) and Down syndrome (12 cf 6 with true CH). The incidence of transient TSH elevation was 6.6 and 5.1/year between 1982–2004 and 2005–15. Of 43 transient cases with CM, 19 involved the digestive system/abdominal wall of which 15 were born ≤ 2004 when iodine antisepsis was largely discontinued in Scottish newborn units.

Conclusion: Infants with low BW, extreme prematurity, sickness, additional malformations, Down syndrome and modest capillary/venous TSH elevation are particularly likely to have transient thyroid dysfunction and merit careful re-evaluation at ≥ 3 years of age. Trends in transient TSH elevation will be influenced by decreases in capillary TSH cut-off, reduced iodine antisepsis usage, and the currently unknown dietary iodine status in mothers.