My adopted cat, Chi, almost died of the same problem. Uroliths already blocked his urinary tract, so he couldn't urinate anymore. I had no idea that he was no longer visiting his litter box because I leave home very early in the morning, and my mom is the one cleaning the box. One day, Chi just suddenly became lethargic. I thought he ate some of the rat poison that my grandfather was leaving all over the compound. I rushed him to the vet. His gums were pale, and he was already very pale. These two signs are very grave.
When we got to the vet, he palpated the bladder and said that the bladder was very distended. What he did was he used a catheter, and helped Chi pee manually. We thought that it was already too late because his urine was so bloody. Good thing our vet was really good. He prescribed a lot of medicines. Sure, the operation and one-month's worth of meds were very expensive but everything turned well in the end.
To not experience this again, make sure that your cat will no longer eat dry kibbles. Give him canned food that is low in protein but high in moisture content. Check how many times he/she pees every day, too.
