Cat illness

Question
Eight days ago my cat slept in some bushes next to my house. She jumped off the porch about four pm since my grandchildren were trying to play with her. We all came in but I did not find my cat until about 8 or 9 pm sleeping in the straw. This was unusual since she is a house cat but does go out on porch sometimes.
Since I found her we have been to Vet and given medicine for urinary track infection. Yesterday she was given a cortizone treatment by vet. Blood work and x-rays do not seem to give the Vet a clue about her illness. She has not eaten food at all. She does drink a little water. She has a low mournful sounding cry in place of a meow. She certainly does not seem to feel well and even though no diagnosis I am ready to euthasnize her since she is approximately 15 years old. Have you seen an old cat die in a manner such as this ie just old age? Thanks for a comment if you can. Pat

Answer
Hi Pat!  Although 15 years of age is definately in the "senior years", old age doesn't suddenly hit like this.  You would usually see her deteriorating slightly and then little by little.
Are you sure there was nothing she could have gotten into outside?  Poisonous plants, anifreeze, rat poison?  Anything that could have caused a toxicity? Is it very hot there, that when she was outside, she could have gotten "heat stroke" or just be dehydrated?  These things more than likely wouldn't cause anything abnormal in the bloodwork.  X-rays would have given hint to any abnormalities like tumors, ect. so that's ruled out.  
Has she been on fluids?  Sometimes when there is a "mysterious" illness present, IV Fluids will help flush out whatever is causing the ailment.  You may want to talk to your veterinarian about that.  They can even give you Subcutaneous Fluids to take home and do at home if you want.  Without eating and only drinking a bit, she surely has to be dehydrated.  The fluids may be all she needs to bounce back.
I wish I could be of more help.  Please, if you have time, let me know how she is doing!
Hang in there!
Hilary