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Fasting decreases thyrotropin responsiveness to thyrotropin-releasing hormone: a potential cause of misinterpretation of thyroid function tests in the critically ill.
J Clin Endocrinol Metab. 1983 Aug; 57(2):380-3.JC

Abstract

We have previously reported that caloric deprivation inhibits peripheral T4 metabolism and blunts the TSH response to TRH in euthyroid obese subjects. To determine whether these phenomena also occur in hypothyroid subjects, T4, T3, rT3, and the TSH response to TRH were measured initially and after a 60-h fast in seven hypothyroid patients. Short term fasting caused a 29% decrement in the maximum serum TSH increment and a 32% decrement in the integrated TSH response to TRH (P less than 0.01). In two subjects with mild hypothyroidism, basal TSH as well as the TSH response to TRH were reduced to levels within the normal range. Specifically, basal TSH values decreased from 7.6 to 3.5 microU/ml and from 11 to 4.1 microU/ml. In the seven subjects, mean serum T3 decreased significantly from 88 to 60 ng/dl, (P less than 0.05) and rT3, initially undetectable in six of seven subjects, rose to detectable or low normal values in four of seven subjects, serum T4 remained at 2.7 micrograms/dl during both study periods. We conclude that 1) fasting induces changes in both peripheral thyroid hormone metabolism and the hypothalamic-pituitary axis in hypothyroid individuals which are qualitatively similar to those that occur in euthyroid subjects; and 2) in certain hypothyroid subjects, fasting alone can decrease basal TSH values to within the normal range. If these data can be extrapolated to critically ill subjects whose caloric intake may be diminished, they suggest that basal TSH concentrations in moderately and severely hypothyroid critically ill subjects will accurately reflect the biochemically hypothyroid state. However, mild degrees of hypothyroidism in critically ill subjects might be overlooked due to the lowering effect of fasting or poor caloric intake alone on basal TSH concentrations.

Authors

No affiliation info availableNo affiliation info availableNo affiliation info availableNo affiliation info availableNo affiliation info available

Pub Type(s)

Journal Article
Research Support, U.S. Gov't, Non-P.H.S.

Language

eng

PubMed ID

6408115

Citation

Borst, G C., et al. "Fasting Decreases Thyrotropin Responsiveness to Thyrotropin-releasing Hormone: a Potential Cause of Misinterpretation of Thyroid Function Tests in the Critically Ill." The Journal of Clinical Endocrinology and Metabolism, vol. 57, no. 2, 1983, pp. 380-3.
Borst GC, Osburne RC, O'Brian JT, et al. Fasting decreases thyrotropin responsiveness to thyrotropin-releasing hormone: a potential cause of misinterpretation of thyroid function tests in the critically ill. J Clin Endocrinol Metab. 1983;57(2):380-3.
Borst, G. C., Osburne, R. C., O'Brian, J. T., Georges, L. P., & Burman, K. D. (1983). Fasting decreases thyrotropin responsiveness to thyrotropin-releasing hormone: a potential cause of misinterpretation of thyroid function tests in the critically ill. The Journal of Clinical Endocrinology and Metabolism, 57(2), 380-3.
Borst GC, et al. Fasting Decreases Thyrotropin Responsiveness to Thyrotropin-releasing Hormone: a Potential Cause of Misinterpretation of Thyroid Function Tests in the Critically Ill. J Clin Endocrinol Metab. 1983;57(2):380-3. PubMed PMID: 6408115.
* Article titles in AMA citation format should be in sentence-case
TY - JOUR T1 - Fasting decreases thyrotropin responsiveness to thyrotropin-releasing hormone: a potential cause of misinterpretation of thyroid function tests in the critically ill. AU - Borst,G C, AU - Osburne,R C, AU - O'Brian,J T, AU - Georges,L P, AU - Burman,K D, PY - 1983/8/1/pubmed PY - 1983/8/1/medline PY - 1983/8/1/entrez SP - 380 EP - 3 JF - The Journal of clinical endocrinology and metabolism JO - J. Clin. Endocrinol. Metab. VL - 57 IS - 2 N2 - We have previously reported that caloric deprivation inhibits peripheral T4 metabolism and blunts the TSH response to TRH in euthyroid obese subjects. To determine whether these phenomena also occur in hypothyroid subjects, T4, T3, rT3, and the TSH response to TRH were measured initially and after a 60-h fast in seven hypothyroid patients. Short term fasting caused a 29% decrement in the maximum serum TSH increment and a 32% decrement in the integrated TSH response to TRH (P less than 0.01). In two subjects with mild hypothyroidism, basal TSH as well as the TSH response to TRH were reduced to levels within the normal range. Specifically, basal TSH values decreased from 7.6 to 3.5 microU/ml and from 11 to 4.1 microU/ml. In the seven subjects, mean serum T3 decreased significantly from 88 to 60 ng/dl, (P less than 0.05) and rT3, initially undetectable in six of seven subjects, rose to detectable or low normal values in four of seven subjects, serum T4 remained at 2.7 micrograms/dl during both study periods. We conclude that 1) fasting induces changes in both peripheral thyroid hormone metabolism and the hypothalamic-pituitary axis in hypothyroid individuals which are qualitatively similar to those that occur in euthyroid subjects; and 2) in certain hypothyroid subjects, fasting alone can decrease basal TSH values to within the normal range. If these data can be extrapolated to critically ill subjects whose caloric intake may be diminished, they suggest that basal TSH concentrations in moderately and severely hypothyroid critically ill subjects will accurately reflect the biochemically hypothyroid state. However, mild degrees of hypothyroidism in critically ill subjects might be overlooked due to the lowering effect of fasting or poor caloric intake alone on basal TSH concentrations. SN - 0021-972X UR - https://www.unboundmedicine.com/medline/citation/6408115/Fasting_decreases_thyrotropin_responsiveness_to_thyrotropin_releasing_hormone:_a_potential_cause_of_misinterpretation_of_thyroid_function_tests_in_the_critically_ill_ L2 - https://academic.oup.com/jcem/article-lookup/doi/10.1210/jcem-57-2-380 DB - PRIME DP - Unbound Medicine ER -