Add 59 modifier to the IHC as long as documentation supports that the Flow and IHC is necessary to determine the result. Usually, either IHC or the Flow did not yield a satisfactory result that leads to the other procedure. Documentation is the key, watch out for duplication process. Pay attention for IHC or Flow that yields negative result, that could be the reason why they order more study. The key is, 59 modifier should be justifiable. Assigning 59 modifier without thorough understanding it's purpose opens up potential liability.
2012 NCCI policy for states:
Medicare does not pay for duplicate testing. CPT codes 88342 (immunocytochemistry, each antibody) and 88184, 88187, 88188, 88189 (flow cytometry) should not in general be reported for the same or similar specimens. The diagnosis should be established using one of these methods. The physician may report both CPT codes if both methods are required because the initial method does not explain all the light microscopic findings. The physician may report both methods utilizing modifier 59 and document the need for both methods in the medical record.
If the abnormal cells in two or more specimens are morphologically similar and testing on one specimen by one method (88342 or 88184, 88187, 88188, 88189) establishes the diagnosis, the same or other method should not be reported on the same or similar specimen. Similar specimens would include, but are not limited to:
Revision Date (Medicare): 1/1/2012
X-12
(1) blood and bone marrow;
(2) bone marrow aspiration and bone marrow biopsy;
(3) two separate lymph nodes; or
(4) lymph node and other tissue with lymphoid infiltrate.