ESPE Abstracts (2016) 86 P-P1-920

Lowering of the TSH cut-off Limit Substantially Alters Universally Accepted Key Features of Congenital Hypothyroidism. Reconsideration of the Use of FT4 levels for Diagnosis and Treatment

Alexandra Iliadia,b, Anna Gikab, Dimitris Platisb, Vasiliki Gioglib, Giorgos Chouliarasa, Ioanna Kosteriaa, Paraskevi Kazakoua, Despoina Apostolakia, George Chrousosa, Panagiotis Girginoudisa, Christina Kanaka-Gantenbeina & Antonis Voutetakisa

aFirst Department of Pediatrics, University of Athens, School of Medicine, “Aghia Sophia” Children’s Hospital, Athens, Greece; bDepartment of Biochemical Laboratories, Institute of Child Health, Athens, Greece

Background: The term Congenital Hypothyroidism (CH) describes children with subnormal thyroid hormone levels present at birth. According to literature, CH has an incidence of ~1:1500–1:3000 births with a clear predominance of females (female:male ratio 2:1) and is mainly caused by thyroid dysgenesis (80%). Low FT4 levels have been used as important criteria for CH diagnosis and treatment initiation. The Greek neonatal CH screening program has followed the TSH cut-off lowering-trend, observed worldwide, from the initial 35 to 6 mU/L.

Objective and hypotheses: To assess the impact of the TSH cut-off limit decrease on key CH features.

Method: Medical records of CH patients of the Greek screening program were reviewed.

Results: From 1980–2014 >3.6 million children were screened, 3209 were diagnosed with CH and in 2159 medical records were available. An increase in CH incidence from 1:3500 to 1:435 births was observed with the use of the cut-off limit of 35 and 6 mIU/L, respectively. Using the TSH cut-off limit of 35 mU/L, females comprised 78% of CH patients whereas, using cut-off limits <10 mU/L (i.e., last 15 years) marginal male preponderance was observed. In a total of 1839 patients in whom ultrasonographic data were available, thyroid dysgenesis was observed in only 16%. In patients with severe CH, thyroid dysgenesis, initial TSH >80 mU/L or patients who received a relatively high LT4 dose (>3 μg/kg per day) at the age of three years, ~32%, 13% and 67%, respectively, had normal FT4 levels (>8.5 pg/ml) at diagnosis.

Conclusion: Lowering of the TSH cut-off limit substantially alters the universally accepted key CH features: incidence is higher, male predominance is observed and thyroid dysgenesis is not the main etiology of CH. Lastly, the use of low FT4 values for CH diagnosis or LT4 initiation therapy should be reconsidered.