We have a lab service we were billing with a particular dx and it was being paid. Now Medicare is not covering that dx. We are getting the CO-50 denial. An outside resource is telling one of our billers we can bill with the GY modifer and then drop the balance to the patient instead of writing it off. I was under the impression that modifier was only to be used on services NEVER covered by Medicare such as preventive services. This lab is covered with other diagnosis codes.Would this be improper use of this modifier? My suggestion was get an ABN and bill with the GA modier? 