Billable / Specific Code
ICD-10-CM C4A.121 is the diagnosis code for Merkel cell carcinoma of left upper eyelid, including canthus. This code falls under the section "Melanoma and other malignant neoplasms of skin" within Chapter 2 — Neoplasms (C00-D49). It is a billable/specific ICD-10-CM code that can be used to indicate a diagnosis for reimbursement purposes. Medical coders and healthcare providers use this code to document and classify diagnoses in electronic health records, insurance claims, and clinical databases.
Always refer to the official ICD-10-CM Tabular List for complete coding guidelines. Ensure documentation supports the specificity of the code selected. When in doubt, consult a certified medical coder or the latest CMS guidelines.
Understanding where C4A.121 sits in the ICD-10-CM classification helps ensure proper coding:
Yes, C4A.121 is a billable/specific ICD-10-CM code that can be used to indicate a diagnosis for reimbursement purposes.
C4A.121 is the ICD-10-CM diagnosis code for "Merkel cell carcinoma of left upper eyelid, including canthus". It is used by healthcare providers to classify and document this condition in medical records and insurance claims.
The parent code of C4A.121 is C4A.12 ("Merkel cell carcinoma of left eyelid, including canthus"). C4A.121 provides a more specific classification within this category.
C4A.121 is located in Section C43-C44 — "Melanoma and other malignant neoplasms of skin" within Chapter 2 of the ICD-10-CM Tabular List.
Use C4A.121 when the patients documented diagnosis matches "Merkel cell carcinoma of left upper eyelid, including canthus" and the clinical documentation supports this level of specificity. Always verify with the latest ICD-10-CM guidelines and payer requirements.
The ICD-10-CM code for Merkel cell carcinoma of left upper eyelid, including canthus is C4A.121.
Yes, C4A.121 can be used as a primary diagnosis code since it is billable and specific.
C4A.121 is in Chapter 2 of the ICD-10-CM Tabular List.
Yes, C4A.121 is a valid ICD-10-CM code for the 2026 fiscal year, subject to official CMS updates.