Frequency and necessity of thyroid function tests in neonates and infants with congenital hypothyroidism.

OBJECTIVE The American Academy of Pediatrics recommends frequent thyroid function tests in infants and children with congenital hypothyroidism (CH). Data supporting the recommended frequency are lacking. This review was conducted to assess the validity of these recommendations. METHODS The thyroxine (T4) and thyroid-stimulating hormone (TSH) levels of 50 neonates diagnosed between 1988 to 1993 were reviewed to assess the length of time on a specific dose of levothyroxine. RESULTS 1) Changes in the dose of levothyroxine occurred 35 times during the first year of life for the 39 children treated with .025 mg/day, five times during the first year of life for the 9 children treated with .0375 mg/day, and three times during the first year of life for the 2 children treated with .050 mg/day. 2) These dose changes occurred at varying time intervals. 3) The T4 and TSH levels obtained at visits requiring dose changes were statistically different from the T4 and TSH levels obtained at the previous two visits. The T4 and TSH levels at the two visits before the change in dosage did not differ statistically. CONCLUSIONS 1) An initial levothyroxine dose of .0375 mg/day requires fewer dose changes than a dose of .025 mg/day. 2) A lack of statistical change in T4 or TSH levels obtained at visits before the change-in-dose visit and the variable time span between dose changes necessitate frequent monitoring regardless of the dose of levothyroxine, the previous T4 or TSH levels, or the length of time at a specific dose. 3) These data support the recommendations of the American Academy of Pediatrics regarding the frequency of thyroid function studies during the first 2 years of life.