Pancreatitis is diagnosed with the snap-fPL, the spec-fPL, or an ultrasound. Unfortunately none of them are entirely accurate. The snap is the cheapest and least accurate. The spec is more expensive and is currently probably the best way to go - it's still not very accurate, but it's less expensive and less stressful for the cat than the ultrasound. If the test comes back positive, then it's positive. But if it comes back negative, it might still be positive.
So if you suspect it, I would recommend doing the spec-fPL and seeing what his level is. Treatment is usually cerenia (for nausea), bupe (for pain) and often sub-q fluids to keep their hydration up. I treat Sam with CBD and have found it to be the most successful treatment for him, and it takes the place of both the cerenia and bupe for all but his most severe flares.
As for the ketones - you don't need to check every day, but you do need to check anytime Gizmo isn't eating well.
Oh, and lab tests aside, the symptoms for pancreatitis are usually nausea, vomiting, inappetence, and pain. I can see Sam's pain in the way he sits, and because he'll stop jumping. And his eyes get dilated and he just looks like he's in pain. He also gets super snuggly (and he isn't normally one to snuggle). Thankfully, and unlike most cats, he isn't very good at hiding his pain.