First - how did they collect the sample?
If via cystocentesis - a needle in the bladder - if done poorly, it is possible to get some blood from the puncture.
If done correctly, red blood cells could indicate some sort of infection (very common), inflammation (somewhat common), or neoplasia (growth of any sort; least common) which was ulcerating, resulting in blood in a urine sample.
Urinary tract infections are very common in diabetics of any species. Watch for frequent litterbox trips with small output - infection will irritate the bladder, so the cat thinks it has to go, go, go, but its all gone, gone, gone. If infection or stones, you may see small amounts of blood. Thats another diagnositc clue for the vet.
I wouldn't wait to check with the vet to see if the Clinadrops would deal with this too - there are thousands of bacteria types, and different types need different meds. You don't want him to feel miserable if the Clinadrops won't handle it too.