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ICD-10-CM 2027 diagnosis code

C4A.22Merkel cell carcinoma of left ear and external auricular canal

✓ Billable / specific

C4A.22 is a valid, billable ICD-10-CM code for merkel cell carcinoma of left ear and external auricular canal. It can be reported on claims for dates of service from October 1, 2026 – September 30, 2027.Short description: Merkel cell carcinoma of left ear and external auric canal

Code unchanged since ICD-10-CM took effect on October 1, 2015. Source: official FY2027 ICD-10-CM release from CDC/NCHS and CMS. Page updated September 29, 2026. About our data

About C4A.22

C4A.22 is the ICD-10-CM diagnosis code for Merkel cell carcinoma of left ear and external auricular canal. It belongs to category C4A (Merkel cell carcinoma), block C43-C44 (melanoma and other malignant neoplasms of skin) and chapter 2 (neoplasms). It is billable, so it can be reported on its own for dates of service from October 1, 2026 through September 30, 2027.

Within C4A.2 (Merkel cell carcinoma of ear and external auricular canal), C4A.22 is specifically for Merkel cell carcinoma of left ear and external auricular canal. Related codes cover unspecified ear and external auricular canal (C4A.20) and right ear and external auricular canal (C4A.21).

It is not a CC or MCC, so as a secondary diagnosis it doesn't change the MS-DRG severity level.

In MS-DRG v44.0, it is part of the grouping logic for DRG 595 (Major Skin Disorders with MCC, relative weight 2.0239) and DRG 596 (Major Skin Disorders without MCC, relative weight 1.1071), in MDC 09 (Diseases and Disorders of the Skin, Subcutaneous Tissue and Breast), as a principal or secondary diagnosis. The DRG a claim lands in depends on the principal diagnosis, procedures and any CC/MCC secondary diagnoses.

It has been part of ICD-10-CM since the code set took effect on October 1, 2015 and hasn't changed since.

Before ICD-10, this condition was coded in ICD-9-CM as 209.31 (Merkel cell carcinoma of the face).

Notes that apply from higher levels

Instructions written at a parent level also apply to C4A.22.

Broader instructions also apply from Chapter 2: Neoplasms.

MS-DRG v44.0 grouping

All DRGs →

Inpatient MS-DRGs this diagnosis can group to, as the principal or a secondary diagnosis, depending on the rest of the claim.

MDC 09 · Diseases and Disorders of the Skin, Subcutaneous Tissue and Breast

ICD-9-CM equivalent

Converter →
  • 209.31Merkel cell carcinoma of the faceapproximate

From the CMS 2018 General Equivalence Mappings (GEMs), the final GEMs release.

Code history

  1. 2016
  2. 2017
  3. 2018
  4. 2019
  5. 2020
  6. 2021
  7. 2022
  8. 2023
  9. 2024
  10. 2025
  11. 2026
  12. 2027
  • FY2016 (effective 10/1/2015): Added (first year of ICD-10-CM)
  • No changes since FY2016.

Common questions about C4A.22

Is C4A.22 billable?

Yes. C4A.22 is a billable/specific ICD-10-CM code valid for FY2027 (October 1, 2026 – September 30, 2027).

Can C4A.22 be used as a principal diagnosis?

Yes. The Medicare Code Editor doesn't restrict C4A.22 as a principal diagnosis.

Is C4A.22 a CC or MCC?

No. C4A.22 is neither a CC nor an MCC under MS-DRG v44.0.

What DRG does C4A.22 group to?

C4A.22 is used in the MS-DRG v44.0 logic for MS-DRG 595 (Major Skin Disorders with MCC) and MS-DRG 596 (Major Skin Disorders without MCC). Which one applies depends on whether it is the principal diagnosis and on the rest of the claim.

What is the ICD-9 code for C4A.22?

The CMS General Equivalence Mappings map C4A.22 to ICD-9-CM 209.31.