A diagnosis code is
just a numbered code the insurance industry uses that is universal
in the medical community so they can decide whether they will or won't pay for a particular procedure. If the diagnosis code wrrants having a particular procedure done, then the insurance company will pay for it.
For example, if a patient has knee pain, and the doc wants an X-Ray, the doc will use the Code for "knee pain," and the procedure code for "X-Ray.