This Article Full Text (PDF) Submit a related Letter to the Editor Alert me when this article is cited Alert me when eLetters are posted Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Reprints, Permissions and Rights Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by BARTALENA, L. Articles by PINCHERA, A. Search for Related Content PubMed PubMed Citation Articles by BARTALENA, L. Articles by PINCHERA, A.

Evaluation of the Nocturnal Serum Thyrotropin (TSH) Surge, as Assessed by TSH Ultrasensitive Assay, in Patients Receiving Long Term L-Thyroxine Suppression Therapy and in Patients with Various Thyroid Disorders^*

Cattedra di Endocrinologia e Medicina Costituzionale, University of Pisa (L.B., M.F., L.B., L.G., C.M., A.Pa., F.A.-L., A.Pi) Pisa
Cattedra di Endocrinologia, University of Cagliari (E.M., S.B.) Cagliari, Italy

Address all correspondence and requests for reprints to: Luigi Bartalena, M.D., Cattedra di Endocrinologia e Medicina Costituzionale, University of Pisa, Viale del Tirreno 64, 56018 Tirrenia (Pisa), Italy.

Circadian variations of serum TSH concentrations have been reported, with higher values occurring in the late evening or early morning. In patients receiving long term L-T₄ suppression therapy, it may be important to achieve suppression of TSH secretion throughout the day. To investigate whether undetectable serum TSH values in the morning are associated with undetectable serum TSH levels at night, serum TSH concentrations were measured by an ultrasensitive immunoradiometric assay in 16 normal subjects, 20 hyperthyroid patients, 10 patients with primary hypothyroidism (either untreated or inadequately treated with L-T₄), 1 patient with central hypothyroidism, 10 patients with nontoxic nodular goiter, 5 patients with functioning thyroid adenoma, 20 patients receiving L-T₄ replacement therapy, and 30 patients receiving L-T₄ suppression. In 6 subjects blood was drawn at hourly intervals for 24 h; in 2 normal subjects a major TSH surge occurred between 2300–0100 h, with other minor peaks, and the same pattern was found in two patients receiving L-T₄ replacement, whereas in 2 patients receiving L-T₄ suppression, serum TSH was constantly below the limit of detection of the assay (i.e. <0.07 mU/L). In the remaining patients blood was drawn at hourly intervals between 2300–0200 h and on the next morning before (0830–0900 h) and 30 min after iv TRH administration. In normal subjects, in patients receiving L-T₄ replacement therapy, and in hypothyroid patients, serum TSH values at night were higher than in the morning, with normal responses to TRH in the first 2 groups and exaggerated responses in the latter. The patient with central hypothyroidism had no nocturnal TSH surge and no TSH response to TRH. In all hyperthyroid patients, serum TSH was undetectable both at night and during the day, and none had a serum TSH response to TRH. Among patients with nontoxic goiter, 7 had detectable serum TSH in the morning, with higher values at night, and a normal response to TRH; the remainder had undetectable serum TSH both at night and in the morning, and subnormal or absent TSH responses to TRH. All 5 patients with a functioning thyroid adenoma had undetectable serum TSH levels in the morning and during the night, and subnormal or absent TSH responses to TRH. Of the 30 patients receiving long term (>6 months) L-T₄ suppression therapy, 28 had undetectable serum TSH both during the night and in the morning and unresponsiveness to TRH.

In conclusion, undetectable basal serum TSH levels in the morning are associated with lack of a physiological TSH surge at night (and, in general, with unresponsiveness to TRH administration). Conversely, detectable, although subnormal, serum TSH values in the morning in patients receiving L-T₄ therapy reflect incomplete suppression of endogenous TSH secretion, as indicated by the persistence of a TSH surge during the night.

^* This work was supported in part by Grant 860053.44 from the National Research Council (C.N.R.), Rome, Italy (Progetto Finalizzato Oncologia, Sottoprogetto 10).

Received September 13, 1987.

This article has been cited by other articles:

				M. Helfand and L. M. Crapo Monitoring Therapy in Patients Taking Levothyroxine Ann Intern Med, September 15, 1990; 113(6): 450 - 454. [Abstract] [PDF]

				D. A. Ehrmann, M. Weinberg, and D. H. Same Limitations to the Use of a Sensitive Assay for Serum Thyrotropin in the Assessment of Thyroid Status Arch Intern Med, February 1, 1989; 149(2): 369 - 372. [Abstract] [PDF]