My cat’s belly grew large within a week, it keeps getting thinner, the abdomen feels firm not fluid-filled, still active but defecating less, occasionally loafs, no fever, clear eyes, eats less kibble but still wants human food. Is it FIP, ascites, or indigestion?

A cat with a swollen belly but a thin body could have an intestinal foreign-body blockage, gas buildup, or ascites. A blockage or gas leads to constipation or reduced stool, and the belly feels firm when pressed; a long-standing blockage can cause severe enteritis with vomiting, poor appetite, and abdominal pain.

Also, pressing the abdomen yourself can lead to misdiagnosis, so ascites cannot be ruled out. Ascites is mainly considered to be from FIP or low-protein liver effusion, and a veterinary examination is needed for a definite diagnosis.