i don't have the book right here....but w/o renal involvement (ie just cystitis) theres no way you have a cast of any kind....you sure they didn't just write "wbc's" for cystitis and not wbc casts (which = pyelo)
also....the rbc thing w/ the cystitis is also only rbc's.....you won't get an rbc cast w/o renal involvement (ie any nephritic syndrome)