Boomer just went to the vet for his annual check up and vaccinations. The blood work came back today and he has low thyroid levels. The vet wants to run a Free T4 test at another $60. Can anyone tell me more about hypothyroidism and whether this additional test is necessary/what its for? The main thing I'm finding about hypothyroidism is that it causes weight gain/obesity and that right now is definitely not a problem with him. I haven't had a chance to speak with the vet yet. I just wanted to find out a little more before speaking with her.