I’m not exactly sure as to what you are asking here. Are you referring to the testing of blood levels for when performing some kind of fitness testing (for example checking lactic acid after a fitness test or a specific high intensity routine) or for someone in general? I remember when I was a competitive swimmer our coaches performed these type of blood testing to see what our lactic acid levels were during our training. They had no specific credentials, certifications and/or training that would make them experts in this matter.
Also, type 1 and 2 diabetics do these type of testing all the time in order to check their blood sugar levels.