Something else, Shinja....you mentioned protein loss. Does your vet think this is due to a UTI? If not, then further testing really should be done if he still is losing protein. If he has a protein losing nephropathy, that needs to be managed differently. My Olivia is on B/P meds and aspirin daily and also RX food (and not the renal diets!).
Cathy's Daisy has that as does my Olivia.
Here is some information on the UPC test:
Urine protein to creatinine ratio