In my case, LabCorp sends the test to Viracor. Since LabCorp is the Provider they are responsible for billing the insurance with the appropriate CPT code. Until September 2012 LabCorp used the CPT codes 88184 (x1) 88185 (x2) and my insurance paid. When they switched to 86849 my insurance stopped.
The Unlisted Immunological Procedure code (86849) is to be used ONLY when no other code is available. The AMA still lists CPT codes 88184 and 88185 as the appropriate codes to be used for Flow Cytometry. In our case the NK Cell Functional Assay. The labs that perform this test still list 88184 and 88185 as the CPT code to be used when billing as you have referenced in your post above.
Our efforts to get information and documentation from LabCorp has fallen on deaf ears. We had to appeal through our insurance. In our Level 1 appeal, LabCorp told our insurance company that the AMA made them change their internal codes and when that happened they could no longer use the CPT codes 88184 and 88185.
Since all the labs that perform this test still list 88184 and 88185 as the CPT codes to be used for this test, we have filed a Level 2 appeal.