My insurance company said that I can appeal their initial rejection to cover immunohistochemical antibody slides of biopsies that my GI doctor removed during an endoscopy/colonoscopy.  

I never had to file an insurance appeal. Would anyone have any suggestions. Also, would you know of any resources that validate the importance of this test to examine the mast cells for concentration and abnormalties?

Any information would be appreciated. Thank you.

I have had to write appeals letters for coverage denial.  To do so I called my insurance company and asked for the fax number and address where the appeals go because it is different than the regular claims address.  They have recommended that I both fax and mail it.  There is also a time limit for appeals based on the date of service.  In it I detailed out specific information and pled my case.  In both instances I was able to get it covered.  

Some of my tests have been considered experimental and denied and I ended up paying a considerable chunk of change.  I have wondered if I had written a letter if I could have gotten it overturned.  I left that issue up to the staff at the university to try recoding the original claim, etc. and I ended up going past the appeals date.