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Exploring the use of recombinant human TSH in the diagnosis of central hypothyroidism

Department of Endocrinology, Sahlgrenska Academy at Göteborg University, Sahlgrenska University Hospital, Gröna Stråket 8, SE-41345 Göteborg, Sweden

(Correspondence should be addressed to H Filipsson; Email: helena.filipsson{at}telia.com)

Context: The diagnosis of central hypothyroidism (CH) is often difficult to establish as serum TSH levels may be low, normal, or slightly increased.

Objective: To explore the use of recombinant human TSH (rhTSH) in the diagnosis of CH.

Design: Randomized single-blind clinical trial.

Setting: Outpatient clinic of a tertiary care referral center.

Intervention: A single intramuscular injection of 0.1 and 0.9 mg rhTSH in random order with 1-week interval.

Participants: Eighteen adult patients with pituitary insufficiency and six healthy age-, sex-, and body mass index-matched controls. Six patients had untreated CH (newCH), six had treated CH (CH), and six patients were TSH sufficient (nonCH). Five weeks before TSH stimulation, levothyroxine was replaced with tri-iodothyronine (T₃) for 4 weeks. One week before stimulation, treatment was withdrawn.

Main outcome measures: Thyroid hormones and thyroglobulin (Tg) before and 2, 3, 7, 24, 48, and 72 h after each injection.

Results: In the newCH group, basal free thyroxine (FT₄) levels were lower than in controls (P<0.05). After 0.9 mg rhTSH, the increases in FT₄ and reverse T₃ (rT₃) were less marked in the newCH group than in controls (FT₄±S.E.M. 9.2±0.5 to 19.7±1.2 vs 11.3±0.5 to 27.8.2±2.4 pmol/l, P<0.05). The CH group exhibited reduced basal and stimulated FT₄ compared with the TSH-sufficient groups. Tg increased similarly among all study groups after rhTSH injection.

Conclusion: In this pilot study, patients with untreated CH had lower response to 0.9 mg rhTSH in FT₄ and rT₃ than controls. An rhTSH test may be useful in the diagnosis of CH, but further studies are required.