The unit of service for coding IHC stains (CPT 88342, 88360 and 88361) has changed effective 1/1/2012. Per the AMA and CAP, the unit of service for each IHC stain charge is one unit per different antigen tested and individually reported per different specimen. Whereas, CMS has released an NCCI edit and indicates in its policy manual that pathologists should not report more than one unit of IHC service per specimen for an immunohistochemistry antibody(s) stain, even if it contains multiple separately interpretable antibodies.
That being said, the unit of service assignment could potentially be different for Medicare/Medicaid cases than other insurances. So, applying the new unit of service rules to PIN-4 cocktail stains, following is an example:
The PIN-4 cocktail stain simultaneously detects P504S (AMACR), HMW CK (cytokeratin CK5 and CK14), and P63 antibodies. Although only one application of the primary antibody cocktail stain is required per specimen, each of the three constituent antibodies is distinguishable one from another via color distinction apparent in either the cell nucleus or the cytoplasm. For billing purposes, the following unit of service would apply:
⇒Per AMA/CAP policy: 88342 X 3
⇒Per CMS: 88342 X 1
The same logic applies to the double and triple stains as the first condition is that an antibody must be individually identifiable and reportable as a prerequisite to a separate unit of service charge. Also, it’s important to note that the number of glass slides that are used during any IHC procedure isn't relevant to the assignment of the proper unit of service.
If there is good news in all of this, the AMA via the CPT 2012 text has added clarifying language that special stains (CPT 88312, 88313) are to be coded by block. This should help dispel the policy that some insurances have adopted to allow payment only on a per specimen basis.
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