A century has passed since children affected by congenital hypothyroidism (CHT) were first treated successfully with thyroid extracts. At that time the diagnosis of severe ‘sporadic’ cretinism was based solely on clinical observation, long before measurement of thyroid hormone and thyroid stimulating hormone (TSH) was possible. Treatment success was evident with the dramatic clinical improvement in the growth and activity of these children.1 However, the severe mental retardation failed to improve in those early cases, which led to the conclusion that thyroid hormone is critical for normal neuronal maturation within a critical time window early in life. The introduction of newborn screening for CHT – by measuring TSH or T42 – finally offered a normal mental outcome to children who otherwise would be severely mentally disabled. Actual studies in adult patients from those first screening programs show that early treatment results in a normal IQ in more than 90% of affected patients.3 4 The treatment of CHT based on newborn screening is therefore one of the most successful achievements in paediatrics.

As always, such a success bears the risk of ‘overdoing it’, as the current discussion on TSH cut-offs points out. Stimulated by that early success and with the intention of further improving the programs, the TSH cut-off levels were lowered to facilitate the diagnosis of milder, previously ‘missed’ cases of CHT. Starting with 50 mU/l TSH as the cut-off in the early programs, which were able to identify severe cases of CHT, the current debate discusses a cut-off value as low as 5 mU/l.

A new publication on this critical cut-off range was recently published in the Archives of Disease in Childhood by Korada et al from Newcastle, UK5. Applying …