PROTOCOL

1. Take a basal 2ml clotted or heparinised blood sample.
1. Inject 0.1 mg/kg of TRH slowly i/v over 1 minute.
1. Take a second 2ml of clotted or heparinised blood 4 hours post TRH injection.
1. Separate the serum or plasma before despatch to the laboratory and label the tubes "pre" and "post TRH".

The following interpretation is based on an original paper by Peterson et al (1994).
 

T4 increase post TRH administration	Interpretation
>60%	Non-thyroidal illness/normal cat
>50% <60%	Equivocal result
<50%	Hyperthyroid cat

The test interpretation does not categorise the response to TRH stimulation in cats with both hyperthyroidism and a concurrent non-thyroidal illness. Although this may only represent a relatively small proportion of hyperthyroid cats (Thoday and Mooney, 1992), a biochemical and haematological profile (EPH) would be advisable in all cats with clinical signs suggestive of hyperthyroidism but with a normal serum T4 level. The results of these investigations should be considered alongside the results of the TRH stimulation test.

COMMENTS

TRH is available on prescription as Protirelin (Roche), 0.2mg/vial. This preparation is not licensed in cats and salivation, vomiting, tachypnoea and defecation occur immediately after injection. All adverse side effects are transient and resolve within the 4 hour test period.
 

Test Code	Test Name and Description	Sample
TRHF	TRH Stimulation Test (Feline)	2 x serum or heparin plasma

REFERENCES

PETERSON, M.E., BROUSSARD, J.D. AND GAMBLE, D.A. (1994) Use of the thyrotropin releasing hormone stimulation test to diagnose mild hyperthyroidism in cats. Journal of Veterinary Internal Medicine 8(4) p 279 - 286.

THODAY, K.L AND MOONEY, C.T (1992) Historical, clinical and laboratory features of 126 hyperthyroid cats. Veterinary Record 131 p257 - 264.