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Thyrotropin-releasing hormone stimulation tests in infants
1Division of Pediatric Endocrinology, University of Medicine and Dentistry-New Jersey Medical School, Newark.
Insights
Thyroid stimulating hormone (TSH) response to thyrotropin-releasing hormone (TRH) stimulation helps evaluate infants with suspected primary hypothyroidism. Hyperresponsiveness may indicate neonatal hypothyroidism requiring further study.
Area of Science:
- Neonatal endocrinology
- Pediatric thyroid disorders
- Clinical diagnostics
Background:
- Infants with abnormal newborn thyroid screening require further evaluation.
- Mildly abnormal serum thyroid function tests necessitate precise diagnostic tools.
Purpose of the Study:
- To assess the utility of the TSH response to TRH stimulation in diagnosing primary hypothyroidism in infants.
- To differentiate between normal and hyperresponsive TSH responses to TRH in infants with abnormal thyroid screening.
Main Methods:
- Measured TSH response to TRH administration (7 micrograms/kg) in 68 infants with abnormal thyroid screening.
- Categorized infants into normal (peak TSH ≤ 35 mU/L) and hyperresponsive (peak TSH > 35 mU/L) groups.
- Monitored long-term clinical and biochemical outcomes.
Main Results:
- Mean baseline TSH was higher in the hyperresponsive group (6.8 mU/L) vs. the normal group (4.4 mU/L).
- Mean peak TSH levels significantly differed: 60.3 mU/L in the hyperresponsive group vs. 24 mU/L in the normal group.
- All evaluated infants in the normal group remained clinically and biochemically normal; 14 infants in the hyperresponsive group showed evidence of thyroid dysfunction.
Conclusions:
- TSH response to TRH stimulation is a valuable tool for evaluating infants with suspected primary hypothyroidism.
- Hyperresponsiveness to TRH may represent a form of neonatal hypothyroidism, warranting further investigation and potential treatment.
Abstract:
The TSH response to TRH administration (7 micrograms/kg) was measured in 68 infants (22 premature) who had abnormal thyroid screening tests by the filter paper method and whose serum thyroid function tests were only mildly abnormal. Twenty-eight infants (12 premature) had peak TSH values of 35 mU/L or less and were considered normal (group I). Forty infants (10 premature) had peak TSH values above 35 mU/L and were considered hyperresponsive (group II). The mean age at testing, screening T4, TSH levels that prompted the testing, as well as baseline T4, T3, and free T4 at the time of TRH testing were not different between the groups. The mean (+/- SD) baseline TSH value was greater in group II (6.8 +/- 2.3 mU/L) than in group I (4.4 +/- 2.2 mU/L; P < 0.001). However, there was a great deal of overlap in the individual TSH values (group I, 0.9-10 mU/L; group II, 1.9-10.6 mU/L). Mean peak TSH levels were significantly different in the two groups (group I, 24 +/- 7.7 mU/L; group II, 60.3 +/- 26.1 mU/L; P < 0.001). During long term follow-up, all 25 group I infants available for evaluation have been confirmed as clinically and biochemically normal. No infant diagnosed as normal was later found to have evidence of hypothyroidism. Fourteen infants in group II have had evidence of thyroid dysfunction. We conclude that the TSH response to TRH stimulation is a useful tool for the evaluation of infants suspected of having primary hypothyroidism. Whether hyperresponsiveness to TRH represents a form of neonatal hypothyroidism requiring treatment remains to be determined.