We get our clinical guidelines from the insurer in most cases. The plans that require precertification for x-rays even give us a list of applicable criteria as well as which x-ray CPT codes they will pay for when billed by a chiropractor. It's possible that some insurers will pay for 72050 but not 75052 simply because they've decided that over 5 views is excessive for diagnosis. We keep a list of what is required and covered by each insurer handy.