Serial Measurements of Thyroid Function in Very Low Birth Weight Infants

Cheryl E. Hanna; Terry Kenny; Victoria DeVito; Janet Hiller; John W. Reynolds; Stephen LaFranchi

doi:10.1515/JPEM.1985.1.2-3.133

Serial Measurements of Thyroid Function in Very Low Birth Weight Infants

Cheryl E. Hanna, Terry Kenny, Victoria DeVito, Janet Hiller, John W. Reynolds, Stephen LaFranchi

Research output: Contribution to journal › Article › peer-review

Abstract

To assess thyroid function in very low birth weight infants, serial free thyroxine (free T₄) determinations were made between age one week and 12 weeks using two radioimmunoassay (RIA) kits, Amersham and Clinical Assays, in 18 infants of 28-weeks gestation or less. TSH was normal in all infants. Both assays showed initial free T₄ concentrations well below values in full term infants. The most severely ill babies had free T₄ values which were significantly lower than the least ill babies in the first four weeks of life by the Amersham method only. By 6 weeks of age free T₄ values increased to the range seen in normal term infants at 1–4 months of age. The increase in free T₄ may be a result of maturation of an immature hypothalamic-pituitary-thyroid axis or resolution of the sick euthyroid syndrome. The Amersham kit showed significantly lower free T₄ concentrations compared to the clinical assays kit up to age 6 weeks. Caution must be used in interpreting free T₄ values in VLBW infants in the first month of life in light of the progression of free T₄ into the normal range by 6 weeks of life and differences found between the two free T₄ RIA kits.

Original language	English (US)
Pages (from-to)	133-136
Number of pages	4
Journal	Journal of Pediatric Endocrinology and Metabolism
Volume	1
Issue number	2-3
DOIs	https://doi.org/10.1515/JPEM.1985.1.2-3.133
State	Published - Apr 1985
Externally published	Yes

ASJC Scopus subject areas

Pediatrics, Perinatology, and Child Health
Endocrinology, Diabetes and Metabolism
Endocrinology

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10.1515/JPEM.1985.1.2-3.133

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title = "Serial Measurements of Thyroid Function in Very Low Birth Weight Infants",

abstract = "To assess thyroid function in very low birth weight infants, serial free thyroxine (free T4) determinations were made between age one week and 12 weeks using two radioimmunoassay (RIA) kits, Amersham and Clinical Assays, in 18 infants of 28-weeks gestation or less. TSH was normal in all infants. Both assays showed initial free T4 concentrations well below values in full term infants. The most severely ill babies had free T4 values which were significantly lower than the least ill babies in the first four weeks of life by the Amersham method only. By 6 weeks of age free T4 values increased to the range seen in normal term infants at 1–4 months of age. The increase in free T4 may be a result of maturation of an immature hypothalamic-pituitary-thyroid axis or resolution of the sick euthyroid syndrome. The Amersham kit showed significantly lower free T4 concentrations compared to the clinical assays kit up to age 6 weeks. Caution must be used in interpreting free T4 values in VLBW infants in the first month of life in light of the progression of free T4 into the normal range by 6 weeks of life and differences found between the two free T4 RIA kits.",

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AU - DeVito, Victoria

AU - Hiller, Janet

AU - Reynolds, John W.

AU - LaFranchi, Stephen

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AB - To assess thyroid function in very low birth weight infants, serial free thyroxine (free T4) determinations were made between age one week and 12 weeks using two radioimmunoassay (RIA) kits, Amersham and Clinical Assays, in 18 infants of 28-weeks gestation or less. TSH was normal in all infants. Both assays showed initial free T4 concentrations well below values in full term infants. The most severely ill babies had free T4 values which were significantly lower than the least ill babies in the first four weeks of life by the Amersham method only. By 6 weeks of age free T4 values increased to the range seen in normal term infants at 1–4 months of age. The increase in free T4 may be a result of maturation of an immature hypothalamic-pituitary-thyroid axis or resolution of the sick euthyroid syndrome. The Amersham kit showed significantly lower free T4 concentrations compared to the clinical assays kit up to age 6 weeks. Caution must be used in interpreting free T4 values in VLBW infants in the first month of life in light of the progression of free T4 into the normal range by 6 weeks of life and differences found between the two free T4 RIA kits.

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Serial Measurements of Thyroid Function in Very Low Birth Weight Infants

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