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Immunoradiometric assay of thyrotropin during the first six months of life
H R Boquete1, A M Sequera, M L Celadilla
1Endocrinology Unit, Hospital Municipal Teodoro Alverez, Buenos Aires, Argentina.
Insights
Thyroid-stimulating hormone (TSH) levels in normal infants vary significantly in the first six months. High TSH may not always signal pathology, suggesting a need to re-evaluate normality criteria.
Area of Science:
- Pediatric Endocrinology
- Neonatal Metabolism
- Hormone Assays
Background:
- Thyrotropin (TSH) is crucial for thyroid function and infant development.
- Establishing normal TSH reference ranges in early infancy is essential for accurate diagnosis.
- Variations in neonatal TSH can occur and require careful interpretation.
Purpose of the Study:
- To assess the variation in thyrotropin (TSH) levels during the first six months of life in normal infants.
- To establish preliminary reference ranges for TSH in early infancy.
- To determine the age at which TSH levels normalize to adult ranges.
Main Methods:
- Prospective study evaluating 105 normal newborns.
- Thyroid-stimulating hormone (TSH), triiodothyronine, and thyroxine levels measured at 48 hours of life.
- TSH levels were additionally determined at multiple time points up to 180 days using an immunoradiometric assay.
Main Results:
- Neonatal TSH levels at 48 hours did not follow a normal distribution, with a median of 4.2 mU/l (percentile 97: 17.7 mU/l).
- TSH levels approached normal adult ranges between 30 and 60 days of life.
- Some infants exhibited elevated TSH levels beyond 60 days, suggesting prolonged variation.
Conclusions:
- Elevated TSH levels in infants during the first six months may not always indicate thyroid pathology.
- Current normality criteria for infant TSH may require critical evaluation to prevent unnecessary investigations.
- Understanding TSH variability is key to appropriate neonatal thyroid assessment.
Abstract:
The aim of this preliminary study was to assess variation in thyrotropin (thyroid-stimulating hormone; TSH) levels using an immunoradiometric assay during the first 6 months of life of normal infants. One hundred and five normal newborns (59 females, 46 males) were evaluated for TSH, triiodothyronine and thyroxine at 48 h of life, and TSH was additionally determined at 15 days (n = 42), 30 days (n = 38), 60 days (n = 24), 90 days (n = 28), and 180 days (n = 30). Complete determinations during the total period of the study were obtained in 17 infants. Samples corresponding to the 48-hour period did not exhibit a normal distribution. In this group, percentile 3 corresponded to 0.9 mU/l, the median to 4.2 mU/l and percentile 97 to 17.7 mU/l. Levels of TSH similar to those of the normal adult population were reached between 30 and 60 days of life. Nevertheless, TSH levels of some of the children remained at higher values for a longer period. In summary, our results suggest that high TSH levels might not always indicate an underlying pathology. A critical evaluation of the normality criteria could avoid unnecessary studies and treatments.