Welcome! You posted in exactly the right place.
It may depend on how high your cat's blood glucose levels are and whether there are any other health problems. If you would get a meter and test at home now, you could see whether he is in the low to mid range (200-300) or very high (400-500) If he is in the mid range, you might be able to try the diet route first. With testing, you can also see if you are getting any improvement before you have to leave town, and decide then whether you have to use insulin.
Here is the information on changing from dry:
www.catinfo.org. Here is a food chart. We try to stay under 8-10% carbs:
Janet and Binky’s chart
Here is a list of things needed for home testing:
A human glucometer. Any one that sips and takes a tiny sample is fine. The meters are often free at drug stores; it’s the strips that are expensive. You can, however, buy them on ebay at less than half the price of stores. Lots of people here also like the ReliOn from Walmart. It is an inexpensive meter and its strips are the cheapest around. Try the meter out on yourself or someone else before you try it on your cat. You want to be familiar with it before you poke the cat.
Lancets and a lancet device. Usually, until the ears “learn” to bleed, a 25-26 gauge is good. Any brand will work.
Ketone strips. (Ketostix) Just like human diabetics use. You will sometimes need to test urine if the numbers are high.
Rice sack. Make this out of thinnish sock, filled with raw rice or oatmeal and then knotted. You heat this in the microwave until very warm but not hot. Then heat the ears before poking.
Also nice to have. Flashlight: so you can look at the ears and find the little capillaries that come off the vein running down the ear. Vaseline: Put a tiny smear where you want to poke. It will help the blood bead up.
And some lo carb treats to give your kitty, successful test or not
Lo carb treats
Here is a good beginning site for hometesting:
Newbie hometesting site and a video:
Video for hometesting We have taught hundreds of people how to test over the internet. We would be glad to help you.