Chemotherapy and Radiation Encounter ICD-10-CM codes

When the encounter is solely for the administration of chemotherapy, immunotherapy, or radiation, the guidelines (section I.C.2.e.2) make Z51.11, Z51.12, or Z51.0 the first-listed diagnosis, followed by the malignancy being treated, for example Z51.11 then C50.911. Z51.11 is for cytotoxic chemotherapy, Z51.12 for immunotherapy including checkpoint inhibitors and CAR-T infusions, and Z51.0 for external beam radiation. When a patient receives more than one of these on the same day, report each applicable Z51 code in any order. These three codes are among the Z codes that may only be reported as first-listed.

Complications that occur during the chemotherapy encounter do not displace the Z51 code: Z51.11 stays first, then the malignancy, then the complication such as R11.2 (nausea with vomiting) with T45.1X5A for the adverse effect. The sequencing reverses when the patient is seen for the complication rather than for treatment. A patient who presents for dehydration (E86.0) from chemotherapy given last week has the dehydration first and no Z51 code; a patient admitted for the complication and given chemotherapy during that stay has the complication as principal with the Z51 code after it.

Oral and maintenance regimens are not encounters for chemotherapy. A patient taking capecitabine or an oral tyrosine kinase inhibitor at home is coded to the active malignancy with a Z79.63x long-term chemotherapy code (added FY2024: Z79.630 alkylating agents, Z79.631 antimetabolites, Z79.632 antitumor antibiotics, Z79.633 mitotic inhibitors, Z79.634 topoisomerase inhibitors). Adjuvant endocrine therapy is Z79.810 for SERMs such as tamoxifen and Z79.811 for aromatase inhibitors; a patient on these is still under treatment and keeps the C code rather than Z85.

Port and line encounters are separate: Z45.2 is the visit for adjustment or flushing of a vascular access device, with Z95.828 for the presence of the port. Z51.81 covers a visit for a drug level. After treatment ends, Z92.21 (history of chemotherapy) and Z92.3 (history of irradiation) are added to the Z08 follow-up visit or to any encounter where prior treatment is relevant.