We recently had a cat Ralf ( name changed to protect his identity ! ) come in because his owner noticed that he was going to the litter tray very frequently and not producing anything. He was getting more agitated.
By the time we saw him that night his stomach was bloated, tight and sore to touch. His bladder was full because he had become blocked. This was an emergency because when blocked the pressure in the bladder can reach back into the kidneys and damage them. Toxins can build up and cats can be dead within 24 hours. The bladder can also rupture.
Ralf was admitted into hospital immediately and anaesthetised. A catheter was placed into his bladder to remove blood stained urine. The urine was tested in our laboratory and struvite crystals were seen. This can be like sand and blocks up a male cats narrow urethra. Female cats do not block up but can get an irritating and painful cystitis The catheter was then removed to assess whether the blockage in his urethra had been removed but unfortunately he still couldn't urinate. The catheter was stitched in place and he stayed with us for three days to allow his bladder to flushed while he was on IV fluids. After three days the catheter was removed and Ralf could urinate by himself again. He was discharged home on special food to try and prevent this from happening again.
Cats blocking up used to be a very frequent occurrence 15 + years ago. There are many causes and these include diets high in particular salts, stress, obesity, and sedentary life style. Most diets have been improved to prevent this but cheaper diets can still be suspect. We now see far fewer cases because of the improvement in diets but it still happens. The patients that get blockages tend to be more difficult to maintain and addressing all the factors of good diet ( prescription urinary diets ), frequently cleaned litter trays, decreased stress, weight loss and more exercise are all key to helping keep this problem away.