Jen, I sure hope that Sterling will recover quickly and that his retest will also go well. If you're worried about your cats developing the calcium oxalate crystals then maybe you should try feeding them Royal Canin Urinary S/O formula. This food is supposed to help prevent both struvite and calcium oxalate crystals. I've been feeding it to Storm, Sunny, and Sky every since Storm had his PU surgery a few years ago.