Recently my 18.5 yr. old cat started urinating outside her box and going more frequently, sleeping excessively, difficulty getting around (back leg weakness), and vomited with diarrhea say before took her to Vet. After bloodwork to check kidney function, Vet started her on antibiotic to treat her for suspected Chronic Pyelonephritis, to continue for 6 weeks. She had a fever over 106 on day of exam. She is responding well to antibiotic, hind end weakness improved somewhat. However, she is eating far less, and continues to lose weight (< 7.5 lbs.). Uses litter box, but still urinating frequently and drinks fair amount of water. Is there a way to tell if she has kidney disease/failure and not pyelonephritis without doing an ultrasound?