Canis ISSN: 2398-2942

Thyroid: TRH stimulation test

Synonym(s): Thyrotropin releasing hormone

Contributor(s): David Bruyette, Roger Powell

Overview

  • Thyrotropin releasing hormone (TRH, from the hypothalamus) stimulates production of TSH from the anterior pituitary to regulate the synthesis and secretion of thyroxine (T4) and tri-iodothyronine (T3)  Hypothalamic-pituitary-thyroid axis diagram . This is a negative feedback system, the released (free) T4 and T3 inhibiting further release of TSH. Using and mimicking this dynamic hypothalamic-pituitary-thyroid axis by ‘excessive’ exogenous stimulation effectively ‘stresses’ thyroid production to highlight any deficiency. It can then be more sensitive than single hormonal measurements. Historically thyroid stimulation tests (TRH and TSH) formed the gold standard reference test for diagnosing thyroid disease, such as canine hypothyroidism.

Sampling

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Tests

Methodologies

  • Measures the T4 before and after i/v TRH injection. Pre and post TSH (with GH) can also be measured.
  • Requires canine specific or validated assays.
  • Varied Fluorescent and Enzymatic ImmunoAssays (EIAs) or RadioImmunological Assays (IRMA / RIAs).
  • Laboratory testing should use external quality assurance schemes to validate performance (eg VEEEQAS / ESVE).

Availability

  • A few in house analyzers and most commercial laboratories for T4 measurement.
  • Most commercial laboratories if also measuring TSH.
  • Few specialist referral laboratories for measuring GH.

Validity

  • Many euthyroid dogs fail to stimulate (any more than hypothyroid cases) in terms of T4 measurements especially. Overall performance no better if not worse than combined T4 and TSH with Free T4 as required to diagnose hypothyroidism. Additional GH measurement may improve the TRH response accuracy but only limited studies to date.

Accuracy

  • TSH % Pre and Post:
    • 90% identifying hypothyroid dogs (relative to euthyroid and sick euthyroid dogs).

Technique (intrinsic) limitations

  • No better accuracy in distinguishing euthyroid from hypothyroid dogs but relatively more time consuming and costly.

Technician (extrinsic) limitations

  • Extravasated TRH administration will not adequately stimulate TSH secretion.

Result Data

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Further Reading

Publications

Refereed papers

  • Recent references from VetMed Resource and PubMed.
  • Pijnacker T, Kooistra H S, Vermeulen C F et al (2018) Use of basal and TRH-stimulated plasma growth hormone concentrations to differentiate between primary hypothyroidism and nonthyroidal illness in dogs. J Vet Intern Med 32(4), 1319-1324 PubMed.
  • Panciera D L (1999) Is it possible to diagnose hypothyroidism? JSAP 40(4), 152-157 PubMed.
  • Scott-Moncrieff J C , Nelson R W (1998). Change in serum thyroid-stimulating hormone concentration in response to administration of thyrotropin-releasing hormone to healthy dogs, hypothyroid dogs, and euthyroid dogs with concurrent disease. JAVMA 213(10), 1435-1438 PubMed.
  • Frank L A (1996) Comparison of thyrotropin-releasing hormone (TRH) to thyrotropin (TSH) stimulation for evaluating thyroid function in dogs. JAAHA 32, 481-487 PubMed.

Organisation(s)

  • Most commercial laboratories.


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