TSH stimulation test
The TSH stimulation test is an adjunct test for determining hyperthyroidism in cats.
Exogenous TSH is a potent stimulator of thyroid hormone secretion. However, serum total T4 concentrations show little or no increase after exogenous bovine TSH administration in hyperthyroid cats. Presumable this is because the thyroid gland of affected cats secretes thyroid hormones independently of TSH control, or that T4 already is being produced at a near maximal rate with limited reserve capacity.
Hyperthyroid cats with serum total T4 concentrations that are equivocally high tend to show results that are indistinguishable from healthy cats . In addition, bovine TSH is no longer available for parenteral administration. Recombinant human TSH has been evaluated in hyperthyroid cats and has a significant cost implication.
Overall, because of its poor diagnostic performance and high cost, the TSH stimulation test is not recommended for hyperthyroidism.
|T3-suppression test||Thyrotropin-releasing hormone (TRH) stimulation test||TSH stimulation test||TSH stimulation test|
|Drug||Liothyronine (Cytomel)||TRH||Bovine TSH||Human TSH|
|Dose||25 µg q 8hr for 7 doses||0.1 µg/kg||0.5 IU/kg||0.025 - 0.20 mg/cat|
|Sampling time||Before and 2-4 hrs after last dose||Before and at 4 hrs||Before and at 6 hrs||Before and at 6-8 hrs|
|Assay||Total T4 and T3||Total T4||Total T4||Total T4|
|Euthyroidism||T4 <20 nmol/L with >50% suppression||>60% increase in T4||>100% increase in T4||>100% increase in T4|
|Hyperthyroidism||T4 >20 nmol/L with <3% suppression||<50% rise in T4||Minimal to no increase||Not determined|
- Mooney, CT, Thoday, KL & Doxey, D (1996) Serum thyroxine and triiodothyronine responses of hyperthyroid cats to thyrotropin. Am J Vet Res 57:987-991
- August, JR (2006) Consultations in feline internal medicine. Vol 5. Elsevier Saunders, USA
- Mooney, CT, Thoday, KL & Dozey, D (1996) Serum thyroxine and triiodothyronine responses of hyperthyroid cats to thyrotropin. Am J Vet Res 57:987-991