I get my ESR tested every month so I know quite a bit about it. It's a test to measure systemic inflammation. Lupus is a classic, systemic, inflammatory disease. Which I have.
Normal ranges are 0-20. If you are having a flare up of a specific inflammatory disease, your number can easily reach 100 or more. Your number of 37 is a sign that something might be going on.
It's a very unpredictable test. Most of the time, it makes a liar out of me! I'll be feeling like crap, and my number is within normal ranges. Or I'll feel really well, and my rheumy will call me and ask how I'm doing because my ESR is elevated...... It's a very frustrating test, and I wouldn't base a lot on it unless the number is at least 60 or more.
Not sure why the nurse said it was a muscle inflammation test. It tests inflammation systemically. So all over the body and in the blood. Not just the muscles.
I don't have any information for you in regards to the CPK test. Sorry!