Just a heads up for those with old cats. My cat Fuzzy who is 14 years old has been losing weight for the last 1.5 years, going from 22 lbs (Mr. Chubby) down to now 11.5 lbs. Eating well and active and regaining activity level as he got thinner (was hunting and active all last summer). The vet did a number of tests to find out what was going on and initially it was thought that it was kidney related as dipstick in urine showed infection. He had an x-ray of the kidneys: no stones or tumors. He was put on a couple different antibiotics (consecutively) but still showing infection. Then the vet did a blood panel which indicated that the kidneys were ok and general health was good. So we got a clean catch urine (my cat peed directly into the test tube in the morning) and they sent out the urine for culture and sensitivities and also a blood sample for thyroid testing. The vet told me that when they see weight loss in elderly cats it is often hyperthyroid which is easy to treat. The culture came back showing he had a treatable infection in the bladder and the thyroid came back hyperthyroid (as expected). High normal for the thyroid is 4.6 and he was 12! Now he is to take one pill a day (very small and cheap) for rest of life.