Hi,
It sounds very much like one of his anal (scent) glands became infected and formed an abscess, which has now burst. It is not an emergency unless he is bleeding profusely, but he will definitely need veterinary attention tomorrow.
If he will tolerate you doing it, I would gently bathe the area so there is no gunge stuck in his fur, and try to stop him licking at it too much.
Also, if you are unsure, you can usually call your emergency vet and ask for advice over the phone without charge.
Eleanor Wood
UK vet
I will let Dr. Krista address your specific blood questions. Were you interested in the holistic approaches to evaluating blood work? Also, not being able to tolerate an occasional eating splurge is considered an early warning sign that a dog is not completely healthy, so there would be many things to do at this point.
I wonder if Cookie has had prior digestive issues?