One missed day is a clue, not yet a verdict
American Shorthairs are famously steady, good-natured cats with healthy appetites, so a refused breakfast is worth attention even though a single off day is commonly harmless. The likeliest explanations are undramatic. The food changed, or the same food came from a freshly opened batch that smells different. The feeding spot moved, visitors disrupted the household, building work raised the noise level, or a warm day flattened everyone's appetite, including the cat's. A hairball working through can also put a cat off food until it passes one way or the other.
Read the rest of the cat before you read the bowl. An American Shorthair that skips a meal but drinks, uses the litter tray normally, grooms, and still supervises the household from its usual chair is a very different case from one that hides, drools, or refuses to be touched.
What to check in the first few hours
Start with the mouth if your cat tolerates a gentle look: a sore tooth, inflamed gum, or something lodged can make eating hurt while hunger remains. You may see the cat approach the bowl with interest, then turn away, chew on one side, or drop biscuits it picked up. That pattern points toward the mouth and deserves a vet appointment even if the cat manages some soft food later.
Check the tray as well. Eating less while urinating normally is one picture; straining, crying, or producing nothing is an emergency at any point, regardless of appetite. Note vomiting and stool changes too, since the combination of not eating plus repeated vomiting moves the timeline up sharply.
The limit: cats should not fast and wait
Cats are not built for prolonged fasting, and overweight cats are at particular risk when they stop eating for an extended stretch, which is why vets set the threshold tighter for cats than for dogs. Use a clear rule: if your American Shorthair has eaten nothing at all for a full day, call the vet, and call the same day, without waiting for that mark, if the cat is a kitten, is senior, has an existing health condition, or shows vomiting, diarrhoea, lethargy, hiding, drooling, or laboured breathing alongside the refusal.
Avoid the temptation to fix the problem with a parade of new foods. A rotating buffet can mask how little is truly being eaten and can upset the stomach further. Offer the normal food, perhaps warmed slightly to release its smell, in the normal quiet spot, and keep water fresh and separate from the bowl's usual competition.
What the vet will want to know
The useful history is a timeline, not a summary: when the last normal meal happened, what has been eaten since, what else changed in the house, and what the tray has shown. Write it down while it is fresh rather than reconstructing it in the consult room. Recording those dated appetite notes in a KinsLe Pet Passport gives your American Shorthair's vet the sequence of events in order, which is often what separates a watch-and-wait plan from immediate tests.