When the patient is presenting for chemotherapy, immunotherapy, or radiation therapy, the primary diagnosis code should be an encounter code which reflects the therapy the patient is receiving at that encounter.
Example:
Z51.0 Encounter for antineoplastic radiation therapy
Z51.11 Encounter for antineoplastic chemotherapy
Z51.12 Encounter for antineoplastic immunotherapy
If the patient is presenting for a follow-up after the treatment has been completed, the provider would report the correct encounter for the follow-up diagnosis code as primary.
Example:
Z08 Encounter for follow-up examination after completed treatment for malignant neoplasm
In addition to the primary diagnoses above, the appropriate diagnosis codes related to the conditions requiring care would also be reported for the services provided.
Selecting a Code Based on Time