Impact of the reduction in TSH cutoff level to 6 mIU/L in neonatal screening for congenital hypothyroidism in Santa Catarina: final results

OUBJECTIVE: To assess the implications of changing the cutoff level of TSH from 10 to 6 mIU/L. SUBJECTS AND METHODS: The study population was constituted by 74.123 children screened for congenital hypothyroidism by the National Screening Program in Santa Catarina, from March 2011 to February 2012. The cutoff of TSH was 6 mIU/L. If TSH between 6-10 mIU/L, the newborn was recalled for a second TSH measurement on filter paper. If TSH > 6 mIU/L in the second sample, the child was sent for medical evaluation. In children with normal topic thyroid, levothyroxine was suspended for 1 month at the age of 3 years for identification of the etiology and evaluation of the need to continue treatment. RESULTS: Among the children screened, 435 were recalled for presenting TSH between 6 and 10 mIU/L in the first sample, 28 remained TSH > 6 mIU/L in the second sample. Among these, 11 had a final diagnosis of dyshormonogenesis, two of ectopic thyroid, two of thyroid hypoplasia and one of transient hypothyroidism. Ten children presented normal TSH levels on the first medical evaluation and two lost follow-up. CONCLUSION: A decrease in the TSH cutoff level from 10 to 6 mIU/L in a neonatal screening program for congenital hypothyroidism reduced the number of false-negative results, increasing the sensitivity of the test, but increased the number of false-positive results and recalls. Since a TSH cutoff level of 6 mIU/L detects thyroid function abnormalities requiring treatment, the adoption of this cutoff level is justified.