Losing weight but lab tests normal.

Dr. Marie replied:

I have had cases like this where a cat is losing weight and hungry and I really suspect hyperthyroidism, yet the thyroid tests and everything else have come back normal. There are a few possibilities.

I can recall one case where I was shocked that the T4 level was normal as I was positive that this was a hyperthyroid kitty. I repeated the test a month later and sure enough, the thyroid level was too high. I don't know if in this case there was a lab error or if the cat's thyroid levels were fluctuating between normal and high and we just happened to catch it on a normal day. It's not a bad idea to consider repeating the thyroid test in a few weeks if no other cause is found.

Unfortunately in an older cat if there are normal blood tests but there is weight loss, vomiting and an increase in appetite there can be some serious causes for these symptoms. There are some types of cancers that can present this way. For example, some types of intestinal cancers can make it difficult for the cat to absorb nutrients from their food and can cause these symptoms. Pancreatic cancer can as well.

There are other pancreas issues that can cause these symptoms that are not caused by cancer, such as chronic pancreatitis. You may want to ask your vet if it is worthwhile to run a feline PLI if this has not already been done. This test is usually good at picking up pancreatic issues.

Another possibility is inflammatory bowel disease. You would expect diarrhea in a cat with IBD. However, there are many cats that will not have diarrhea with IBD but instead will have vomiting and weight loss.

The increase in vocalization doesn't mean much specifically and is common with a number of conditions in older cats. It can be caused by high blood pressure which often goes along with hyperthyroidism. However, high blood pressure can go along with heart disease as well. But, if there was heart disease, your vet likely would have heard a heart murmur on physical exam. It's not a bad idea to have your cat's blood pressure checked just to be sure.

At this point if this were my case, I would be giving you a few options. If your budget allows for it, then the next step would be xrays or possibly even ultrasound to look for evidence of a tumor somewhere. And again, I would likely run a PLI to look at the pancreas and a blood pressure test. Or another option is to wait for a few weeks and then recheck the thyroid levels.

Weight loss in an older cat is always something significant, so it really should be investigated. But I have had cases where we did a lot of tests and could not find anything. Usually when this happens, some type of problem such as a cancer finally turns up weeks or months in the future.

I hope you find some answers soon and I hope everything is ok!

Dr. Marie.


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