Feline TRH Stimulation Test

Indications:

Diagnostic test for the differentiation of normal cats from those with hyperthyroidism despite having a basal T4 within the high normal reference range. The test would be indicated in older cats with appropriate clinical signs/palpable goitre and a persistent high normal basal T4 result.

Note: TRH is not a licensed product for use in the cat.

Principle:

TRH stimulates the release of TSH from the pituitary and results in increased T4 concentrations in normal cats. In hyperthyroid cats release of TSH is inhibited by high T4 concentrations. As a result hyperthyroid cats stimulate very poorly in response to TRH.

Protocol:

• Obtain a baseline separated serum sample
• Administer TRH iv at 0.1mg/kg. This is equivalent to 1ml/kg of a 100ug/ml solution
• Take a second sample 4 hours later

T4 only is routinely assayed in this test.

Warning: Administration of TRH iv is commonly associated with central nervous system signs including salivation, vomiting, tachypnoea and defaecation. These signs are transient and resolve by the time of the second sample.