Urine ketons strips? I used to have a small plastic cup ready, next to each litter box, and I would wait until my boy started peeing. Then, I would go to him slowly with the plastic cup and hold it under his stream. You don't need a lot of urine. I would take the sample back to my bottle of test strips which was under a clock that has a second hand, take one out, dip the test strip into the pee, take it out, and wait the 15 seconds by looking at the clock, then compare the test strip to the key on the outside of the bottle.
The blood ketone test strips are different. Which kind do you have?