Feline Hypothyroidism

Feline hypothyroidism is considered to be a rare condition. Options for diagnosis include the measurement of serum TT4 or Free T4 and TSH (TP1 or TP3 – see canine hypothyroidism), or a TRH stimulation test. A TSH stimulation test would be ideal if a TSH preparation is available (including recombinant human TSH; Thyrogen®, Genzyme; 0.025 to 0.200 mg IV of rhTSH).

The most common form of feline hypothyroidism is iatrogenic following treatment of hyperthyroidism. Less commonly we recognise naturally occurring feline hypothyroidism (both congenital +/- goitre and inflammatory forms exist). The combination of azotaemia and iatrogenic hypothyroidism has been shown have a detrimental effect on the survival of treated hyperthyroid cats.

TRH Stimulation Test

  1. Collect blood for basal TT4 concentration
  2. Inject 100 μg TRH i/v slowly over one minute. Side effects including salivation and vomiting can be seen occasionally
  3. Collect second blood sample 4 – 6 hours later
  4. Label samples clearly and request TT4


Normal cats – post stimulation result is expected to be about 1.5 – 2 times greater than the basal T4 concentration.

Monitoring of feline hyperthyroidism is detailed at the end of the booklet under endocrine therapeutic monitoring.