Related Experiment Videos
Is there compensated hypothyroidism in infancy?
R Alemzadeh1, S Friedman, P Fort
1Department of Pediatrics, North Shore University Hospital-Cornell University Medical College, Manhasset, NY.
Insights
Newborn screening can identify infants with high thyroid-stimulating hormone (TSH) but normal thyroxine (T4) levels. Measuring basal metabolic rate (BMR) helps detect subclinical hypothyroidism in these infants.
Area of Science:
- Pediatric Endocrinology
- Neonatal Screening
- Metabolic Studies
Background:
- Newborn screening programs identify infants with potential thyroid dysfunction.
- Some infants present with elevated thyroid-stimulating hormone (TSH) but normal thyroxine (T4) levels, a condition requiring further investigation.
- The clinical significance of isolated hyperthyrotropinemia in neonates is not fully understood.
Purpose of the Study:
- To investigate the thyroid status of infants identified with normal thyroxine (T4) and elevated thyroid-stimulating hormone (TSH) through newborn screening.
- To determine if basal metabolic rate (BMR) can identify subclinical hypothyroidism in these infants.
- To assess the response to thyroid therapy in infants with low BMR and hyperthyrotropinemia.
Main Methods:
- Studied 10 infants (9-63 days old) with normal T4 and varying TSH levels using indirect calorimetry to measure basal metabolic rate (BMR).
- Clinically assessed infants for euthyroid status and biochemical markers of hypothyroidism.
- Monitored BMR and TSH levels before and after thyroid therapy.
Main Results:
- Four infants had a low BMR (38.1 kcal/kg/day) and TSH levels >7.0 microU/mL; six infants had normal BMR (49.6 kcal/kg/day) and TSH levels <6.0 microU/mL.
- Infants with low BMR showed normalization of BMR (48.7 kcal/kg/day) and TSH suppression (3.2 microU/mL) within 3 weeks of thyroid therapy, with sustained normal T4 levels.
- These findings suggest a hypometabolic state in infants with normal T4 but elevated TSH.
Conclusions:
- Basal metabolic rate (BMR) assessment is a valuable tool for identifying subclinical hypothyroidism in infants with normal thyroxine (T4) levels and elevated thyroid-stimulating hormone (TSH).
- Monitoring BMR alongside TSH levels can aid in defining and managing this condition.
- Thyroid replacement therapy effectively normalizes metabolic rate and TSH in these infants.
Abstract:
The state-mandated newborn thyroid screening program may uncover infants who exhibit normal thyroxine (T4) levels with various degrees of hyperthyrotropinemia. To elucidate further the thyroid status, the basal metabolic rate (BMR) of 10 infants (7 boys, 3 girls; aged 9 to 63 days) was studied by indirect calorimetry. They were clinically euthyroid and healthy with no evidence of overt biochemical hypothyroidism (low T4, high thyroid-stimulating hormone [TSH]). Confirmatory testing indicated that all infants had normal serum T4 levels for age (mean +/- SD: 10.3 +/- 3.2 micrograms/dL). However, serum TSH levels varied from 2.3 to 99.2 microU/mL. In 4 infants (2 boys, 2 girls) the BMR was low (38.1 +/- 4.1 kcal/kg per day), while the other 6 patients (5 boys, 1 girl) demonstrated BMRs within the normal range (49.6 +/- 1.9 kcal/kg per day, P less than .001). The serum TSH levels were above 7.0 microU/mL among those infants with a low BMR, whereas the serum TSH levels were always below 6.0 microU/mL among the normometabolic infants. All infants who had a low BMR received thyroid therapy and promptly became normometabolic (BMR: 48.7 +/- 1.0 kcal/kg per day) with suppression of TSH levels (3.2 +/- 1.3 microU/mL) within 3 weeks of therapy, while their serum T4 levels remained within the normal range. The observed normalization of BMR in parallel to reduction of TSH levels following thyroid replacement therapy strongly suggests that these patients demonstrated a hypometabolic state, despite normal serum T4 levels. Therefore, the assessment of BMR may help define subclinical hypothyroidism in infancy in conjunction with a close monitoring of TSH concentration.