Coding and reporting for immunohistochemistry (IHC) staining in dermatology

By Faith C. M. McNicholas, RHIT, CPC, CPCD, PCS, CDC, Manager, Lead Coding and Reimbursement Strategist, July 1, 2022

Academy coding staff address important coding topics each month in DermWorld Coding Consult. Read more Derm Coding Consult articles.

Immunohistochemistry (IHC) staining is used to detect the presence of markers that can assist with accurate tumor classification and diagnosis. IHC has evolved to complement the hematoxylin & eosin (H&E) and special stain techniques that typically show tissue and cellular morphology (structure) with the goal of reaching a more accurate diagnosis. Although dermatologists frequently report IHCs, there is still some confusion concerning the proper CPT^® coding and medical record documentation for immunohistochemistry staining.

Medicare and private payers have coverage policies that provide detailed guidance on documentation and coverage requirements for reporting IHCs. Mohs Micrographic Surgery (MMS) (17311-17315) codes include staining with routine stains (i.e., H&E and toluidine blue). Although generally not separately reimbursable when reported on the same date of service (DOS), under acceptable indications, surgical pathology codes (88300-88309, 88329-88332, 88341-88344) can be billed on the same DOS as Mohs surgery. It is important to note that IHC pathology codes 88341-88344 should be used only when diagnosis cannot be determined on routine H&E staining. If additional non-routine histochemical stains (88314) are performed, these can also be separately reported, once per block.

IHC service can be reported during, but is not limited to, the following scenarios:

• Margin evaluation in Mohs surgery sections;

• Detection of atypical melanocytes on frozen sections;

• Detection of perineural keratinocyte-derived tumors.

When 88314, 88341, 88342, and/or 88344 are reported, there must be medical record documentation demonstrating the medical necessity for the procedure on file. There are circumstances when a payer may request a review of the record — post-service — to determine medical necessity. When medically necessary immunohistochemistry codes are billed on the same date of service as MMS, all criteria in the guideline titled “Immunohistochemistry (IHC)” apply.

IHC reporting guidelines

Because reporting IHC can be complex, understanding the ‘how to’ and ‘interpretation of the definitions’ can make coding and reporting IHC less complicated.

IHC codes are reported with the following codes:

88342 Immunohistochemistry or immunocytochemistry, per specimen; initial single antibody stain procedure

88341 Each additional single antibody stain procedure
(List separately in addition to code for primary procedure)

88344 Each multiplex antibody stain procedure
(Do not use more than one unit of 88341, 88342, or 88344 for the same separately identifiable antibody per specimen)

Defining the ‘specimen’

According to AMA CPT, a specimen is defined as tissue or tissues that is (are) submitted for individual and separate attention, requiring individual examination and pathologic diagnosis.

• Although the specimen definition is listed under surgical pathology, preceding the 88300 – 88309 histopathology code series in the AMA CPT Coding Manual, the definition applies to all other pathology codes that include the word “specimen” in their descriptors. This contrasts with the “block” definition used for the Mohs surgery coding, where separate pieces embedded together count as a single "block."

AMA CPT further states that two or more such specimens from the same patient (e.g., separately identified endoscopic biopsies, skin lesions) are each appropriately assigned an individual code reflective of its proper level of service.

Examples of IHC specimen can be described as:

• One large Mohs stage excised as one piece, quadrisected and processed as four blocks, with each block stained with IHC: one specimen; OR

• Two separate, discontiguous margin pieces of tissue excised, each processed separately and stained with IHC: two specimens.

Reporting IHC

To determine the appropriate reporting for either a single or multiplex antibody staining, it is helpful to understand CMS’ guidance in chapter 10, page 23 of the 2022 NCCI policy manual which states the following:

“The unit of service for immunohistochemistry/immunocytochemistry (e.g., CPT codes 88342, 88341, and 88344) is each single or multiplex antibody stain procedure per specimen.

A multiplex antibody immunohistochemical staining procedure is one that uses multiple antibodies to obtain multiple separately reportable medically reasonable and necessary results.

An antibody stain containing multiple antibodies that yields a single reportable result is not a multiplex stain and shall be reported with a single antibody staining procedure CPT code.

An immunohistochemistry stain procedure with multiple antibodies that are not separately interpretable (e.g., antibody cocktail) shall only be reported as one unit of service per specimen.

If a single immunohistochemical/immunocytochemistry stain procedure for one or more antibodies is performed on multiple blocks from a surgical specimen, multiple slides from a cytologic specimen, or multiple slides from a hematologic specimen, only one unit of service shall be reported for each separate specimen.”

IHC with Mohs surgery

There is specific coding guidance for reporting IHC with Mohs surgery. The 2022 NCCI Policy Manual, chapter 3, page 15, states:

If a Mohs surgeon removes a tumor specimen and divides it into multiple pieces of tissue, creates a block from each piece of tissue, and stains one or more blocks from that specimen with an initial single antibody immunohistochemistry stain, the Mohs surgeon shall report only one unit of service of CPT code 88342 (immunohistochemistry or immunocytochemistry, per specimen; initial single antibody stain procedure). Only one unit of service of CPT code 88342 may be reported per specimen.

If the Mohs surgeon additionally stains one or more blocks from that specimen with an additional different single antibody immunohistochemistry (immunocytochemistry) stain, CPT code 88341 (immunohistochemistry or immunocytochemistry, per specimen; each additional single antibody stain procedure (list separately in addition to code for primary procedure)) may be reported with one unit of service per different antibody stain procedure. The unit of service for these codes is not each block derived from a single specimen.

Remember, the UOS for IHC codes is the specimen and not each block derived from a single specimen.

General coding policies

Like every other CPT code, the IHC codes also have Medically Unlikely Edits (MUE) values and NCCI PTP edits. These are based on services provided by the same physician to the same beneficiary on the same date of service. Exceeding the MUE for a particular DOS could result in claim denial and may warrant an appeal with medical record documentation submitted to the payer.

Dermatologists should note the Medicare NCCI policy discourages physicians from inconveniencing or increasing risks to beneficiaries by performing services on different dates to avoid MUE or NCCI PTP claim edit denials. Splitting the service to multiple DOS to avoid MUE based claim denials can result in adverse Medicare action.

The table below shows the current MUE values for IHC:

Documentation requirements

To justify medical necessity, always document:

• why additional (IHC) testing was done;

• the results of stains, and how the information was used by the treating physician.

Example 1

You perform the first stage of Mohs surgery for a lentigo maligna on the left cheek. The excised tissue is quadrisected and each of four pieces is processed on a separate block. Immunohistochemical staining of each block is done with Melan-A.

You report:

17311 Mohs surgery, first stage
88342 - 59* Initial antibody stain

* Based on NCCI guidelines, modifier 59 is appended to the initial antibody stain code (88342).

Example 2

Same as in example 1, the first stage of Mohs surgery for a lentigo maligna is performed on the left cheek. The excised tissue is quadrisected and each of four pieces is processed on a separate block. In this example, immunohistochemical staining of each block is done with Melan-A and SOX-10.

• Two separately identifiable and separately interpretable IHC stains are done.

• Only one (quadrisected) specimen, the entire excised tissue piece, is evaluated.

You report:

17311 Mohs surgery, first stage
88342 - 59* Initial antibody stain
88341 Additional antibody stain

Remember that each 88341 code must be billed on a separate line to avoid claim denial.

*Based on NCCI guidelines, modifier 59 is appended to the initial antibody stain code (88342).

Example 3

The first stage of Mohs surgery for a lentigo maligna on the left cheek is excised and quadrisected. Each of four pieces is processed on a separate block. Immunohistochemical staining of each block is done with Melan-A. Melanoma is identified in superior and inferior margins. Two separate tissue specimens are excised from these margins and processed and interpreted independently.

You report:

17311 Mohs surgery, first stage
17312 Mohs surgery, second stage
88342 - 59 Initial antibody stain, first specimen
88342 - 59 Antibody stain, second stage, specimen 1
88342 - 59 Antibody stain, second stage, specimen 2

Example 4

Multiplex antibody IHC stain with the following stains

Pan melanoma and S-100

• Two separately identifiable antibodies in one application.

• Two stain colors differentiate the two antibodies.

When one specimen, two separately identifiable stains are used, report CPT code 88344.

Example 5

Antibody cocktail IHC stain

Two antibodies mixed, one stain (pancycytokeratin, Ae1/AE3). In this case, individual antibodies cannot be separately identified.

The service would be reported with CPT code 88342.

Example 6

If slides from each Mohs block are stained with H&E and Melan-A, you would report:

17311 Mohs surgery, first stage
88342 - 59 Immunohistochemistry, one specimen, one stain

For more on IHC coding, view chapters 3 and 10 in the CMS NCCI Policy Manual, and the CMS Special Histochemical Stains & Immunohistochemical Stains LCD.

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