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Frequency and necessity of thyroid function tests in neonates and infants with congenital hypothyroidism
1Department of Pediatrics, Baylor College of Medicine, Houston, TX 77030, USA.
Insights
Frequent thyroid function tests are necessary for infants with congenital hypothyroidism (CH). This study found that monitoring is crucial regardless of levothyroxine dosage due to variable T4 and TSH levels, supporting current guidelines.
Area of Science:
- Pediatrics
- Endocrinology
- Neonatal care
Background:
- The American Academy of Pediatrics recommends frequent thyroid function tests for infants and children diagnosed with congenital hypothyroidism (CH).
- Limited data currently exist to support the recommended frequency of these tests.
Purpose of the Study:
- To assess the validity of current recommendations for the frequency of thyroid function testing in infants and children with CH.
- To evaluate the relationship between levothyroxine dosage, thyroid hormone levels, and the need for dose adjustments.
Main Methods:
- Retrospective review of thyroxine (T4) and thyroid-stimulating hormone (TSH) levels in 50 neonates diagnosed with CH between 1988 and 1993.
- Analysis of the time intervals between levothyroxine dose changes and corresponding T4/TSH levels.
Main Results:
- Levothyroxine dose adjustments were frequent, particularly in the first year of life, with varying intervals between changes.
- Thyroid function tests (T4 and TSH) at visits requiring dose changes were statistically different from previous levels.
- No statistical difference was observed in T4 or TSH levels between the two visits preceding a dose change.
Conclusions:
- An initial levothyroxine dose of 0.0375 mg/day required fewer adjustments than 0.025 mg/day.
- Frequent monitoring of thyroid function is essential for infants with CH due to unpredictable changes in T4 and TSH levels, irrespective of dosage or prior test results.
- The findings support the American Academy of Pediatrics' recommendations for frequent thyroid function testing in the first two years of life for children with CH.
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.
