As I have mentioned... I have a hard time getting my cat to submit to an exam... and absolutely NO blood. But I have a super easy time getting my cat to allow a urine test. I just put a plastic trash bag over my cats litter box. He doesn't seem to recognize anything has changed with the plastic bag.

So I did that... got urine and took it in.

This tells two things generally (exclusion diagnosis).

Kidney issues-- as if the urine is concentrated it suggests the kidneys are working fine.
and
Glucose in the urine. Which is suggestive of diabetes. My last blood tests the glucose came back very high. The vet suggested that there was no need to worry as diabetes is very unlikely without glucose in the urine. He said high blood sugar is due to stress.

Both came back in good shape. Urine was concentrated and there was no glucose in the urine. So I know before I even get the exam that two big issues are out and it is safe to give my cat the sedative they have prescribed for him.