The enzyme in the blood that indicated muscle damage is called cpk.
There are a few reason you will get false high readings of cpk which are very typical in your situation and I have experience many times.

False high reading of cpk can happen because miss handing of the blood sample, ( the sample gets bumped around too much before it gets to the lab)
also taking several samples or looking for a good spot to get blood will cause the cpk to rise, this is common when a vet goes hunting to get a blood sample but misses a few times before he actually gets the sample.

What was the white and red blood cell count?

What was the calcium level?

What was the uric acid?

What was the total Protein?

Other suggestions on the thread seem like a good start.