Q: My ferret recently became very lethargic. He more or less lies in his hammock with a distant look on his face. He was taken to the vet today and given a full blood work evaluation. Everything came back well within norms except for the T4 thyroid test. He had a 1.6 value, which my veterinarian said was a little low but still within normal ranges. My veterinarian has never had a hypo/hyperthyroidism case before, and is still going to investigate.
I would like to know where the 1.6 score puts my ferret. What is the treatment if he does have hypothyroidism? He is eating, drinking and doing all other functions regularly.
A: Both hypothyroidism and hyperthyroidism have not been described in ferrets as a common or even rare disease. Let’s be thankful there is one endocrine gland that remains normal in ferrets!
Hypothyroidism is very difficult to diagnose, even in animals that we know get this disease, such as dogs. It is more common in certain breeds. Because this disease is difficult to diagnose, veterinarians use many blood tests to diagnose hypothyroidism. The resting thyroid level, which is the test your doctor did on your ferret, is a screening test. If this test is abnormal, it indicates that further tests need to be done. Also, a few different methods are used to measure thyroid levels, and some are more likely to be accurate than others.
If this were a dog with a slightly low number, the next step would be to consider a few more specific tests, and possibly a stimulation test. A stimulation test is given to the patient to try to force the thyroid to produce more thyroid hormone. If this stimulation test does not elicit the correct response, than a diagnosis of hypothyroidism can be made.
Because we do not see hypothyroidism in ferrets, the stimulation test is rarely performed. Interestingly enough, though, a protocol exists for performing this test in ferrets.
Based on a 1.6, it is highly unlikely your ferret has hypothyroidism. This number should be much lower if it is hypothyroidism. Because hypothyroidism is a very rare disease, the odds are stacked against your ferret having it. It may be worthwhile to investigate other avenues of disease diagnosis. If you believe, however, that there is a good chance this is hypothyroidism, then the stimulation test may be your next step.