Canine TRH Stimulation

Indications:

As an aid to the diagnosis of hypothyroidism in the dog.

Notes:

• This test should only be performed on dogs whose clinical history, physical examination, and routine haematology/biochemistry findings are consistent with hypothyroidism.
• Where possible, drugs likely to affect thyroid function (including glucocorticoids, potentiated sulphonamides, anaesthetics, sedatives, frusemide, mitotane, NSAIDS and thyroxine) should be withheld for at least four weeks before testing.
• Chronic sulphonamide and thyroxine therapy may require more extended withdrawal periods. Please contact the laboratory for further information.
• Hyperadrenocorticism (Cushing's disease) can be associated with significant reductions in basal T4 and thyroid responsiveness in euthyroid dogs. If clinical signs could reflect Cushing's, it is advisable to exclude this endocrinopathy initially before further evaluating thyroid function.
• Side effects of TRH when used at this dose are very uncommon and, if they do occur, are mild (e.g. salivation, defecation). Atropine is an effective antidote if any side effects cause a problem.

Protocol:

• Fast patient overnight.
• Take 1-2 ml blood (plain/gel tube) as baseline sample. Ensure sample has clotted fully. Separate serum within 30 minutes.
• Inject TRH (intravenously). See table below for suggested dosage.
• Take second sample (plain/gel) tube 4-6 hours post injection. Ensure sample has clotted fully. Separate serum within 30 minutes.
• Label tubes with patient’s name and time when the samples were taken.
• Send both samples to the Laboratory.