how can i tell which cat is sick?

one of the four cats in my house had bloody pee with crystals in it. i've been watching all of them for symptoms tonite, but they all seem to be acting totally normal. i plan to check them all for fevers first thing in the morning when i can get a thermometer. there's a chance that it won't cause a fever though. i know this can be serious. is there any way to tell who needs treatment?

Asked by Pippa on Jan 16th 2013 in Health & Wellness