Hi! I'm CalCatDoc and help with your questions about Ckiku.
I'll need to ask a few questions to get a better feel for the situation Do you recall which of the liver tests showed the 119? If it was the ALT, that number is XXXXX barely above normal so by itself it doesn't raise any red flags if the cat is well and not vomiting or losing weight. It does, however, need to be monitored over time in case it is an indication of something starting to go wrong.
As far as the borderline high thyroid hormone level goes - again, given that he is obese, if he isn't actually doing any unplanned weight loss or having a vomiting problem, it is just something that should be looked at again down the road. The one thing that all truly hyperthyroid cats have is weight loss (other symptoms vary).
I think your vet's recommendation makes sense. If you are really concerned, you could do the repeat lab work in 3 or 4 months rather than 6. You want to be sure to have them do a urinalysis at the same time - I always look at both blood and urine tests unless we are following a limited number of individual numbers. Urine specific gravity is a vital indicator of kidney function and shows trouble long before the blood tests will.
It sounds like he is one of those lucky older cats that has managed to escape major problems in his older years. Science Diet is an excellent choice for his food and probably has a lot to do with his good health.
Do watch out for any appetite problems or lethargy/weight loss because those can be a sign that there is a legitimate liver problem. And weight loss in and of itself raises concern about the thyroid, and also kidney problems and diabetes (which obese cats are at increased risk of).
Please bookmark this page so you can navigate back here easily. If you have any additional questions or concerns, you can continue this conversation with me in Q&A mode rather than live chat. I hope this has been helpful and reassuring to you.