Update on Tigger, my 20+ boy who has all the symptoms of an over-active thyroid:
The test shows his thyroid is totally normal. However, as his heart is beating with what the vet calls a "galloping heart murmur" his Tiggerness will be starting on a small dose of a heart med and then get rechecked in 2 weeks to see how he is doing. In the meantime, I'm to obtain a poop sample to be checked. His urine already showed some blood and white blood cells from his chronic renal failure but he no longer tolerates any oral antibiotics so for now the low level UTI gets benign neglect rather than treatment. The vet is looking into a new injectable antibiotic that lasts for 2 weeks at a time to see if it is appropriate, does not have side effects Tigger can't tolerate, is available, and is even remotely affordable.
So, the old man gets some heart medicine, gets to keep eating me out of house and home, and a recheck in a couple of weeks.