Hello and thank you for your question.
Increase in CPK levels suggests that you might have damage to the muscle tissue.
when a muscle is damaged, CPK leaks into the bloodstream. Determining which specific form of CPK is high helps doctor's determine which tissue has been damaged.
As you had back surgery that can be one reason as having a history of lower back pain and if have nerve compression in lower back can also affect the muscle activity. These can also cause high CPK levels.
I would suggest to follow up with your doctor regularly to monitor these levels.
Please get back to me if you have any further questions. My goal is to provide an excellent service and I would be happy to answer your questions. Thank you.