We have had 3 cats with advanced (but not total) renal failure-- two Siamese and a shorthair: The LEAST successful case lived two and a half years (from age 18 to age 20-1/2) on sub-cutaneous fluids, happy, active, healthy, and loving life; one lived FIVE wonderful happy years that way. DO NOT DESPAIR, especially if your Persian is a friendly mellow lap-cat! It can be dealt with! They used to just lie stretched out on my legs while I had my feet on a table, and I would hang an IV bag of WARMED (to cat body temp or close) lactated Ringer's solution on the door behind me and give the cat fluids sub-cu. (in the loose-skin area behind the scruff) while skritching her under the chin and petting her and she would purr and lie there and be totally happy-- a couple of hours for the fluid to be absorbed and she was good as new and VERY happy and active! It works wonderfully-- so don't give up hope! Your little friend may have a LOT of good years left, and I DO mean GOOD years!! Those cats were totally happy, 100%, no 'suffering' involved whatsoever...... believe me......
Wait and see what the blood-work and the vet say......
GOOD LUCK--