C79.00
BillableSecondary malignant neoplasm of unspecified kidney and renal pelvis
Last updated: FY2026 ICD-10-CM (Oct 1, 2025 – Sep 30, 2026) | CMS-HCC V28 (100% phase-in, PY2026)
Is C79.00 an HCC code?
Yes. C79.00 maps to Metastatic Cancer and Acute Leukemia under the CMS-HCC V28 risk adjustment model (and Metastatic Cancer and Acute Leukemia under V24).
HCC Category Mapping
RAF weights shown are the community, non-dual, aged base weights from the CMS risk adjustment model file. Actual per-patient RAF contribution depends on member segment, interactions, and the model year used by the payer. V28 is the CMS-HCC model phased in over payment years 2024–2026; V24 remains in use during the transition and for historical data.
MEAT Criteria for C79.00
For C79.00to count as a valid HCC diagnosis in a given encounter, the provider's documentation must show MEAT: Monitor, Evaluate, Assess, or Treat. A diagnosis from a prior year does not carry forward automatically — it has to be re-documented and supported each calendar year.
- MMonitor: signs, symptoms, disease progression, or lab trending documented in the note
- EEvaluate: test results, medication response, or physical findings reviewed by the provider
- AAssess: explicit mention in the assessment or plan with acknowledgment of status
- TTreat: medication, referral, procedure, therapy, or counseling tied to the diagnosis
Only one of M/E/A/T is required to support the code, but the documentation must be specific enough to show that the provider actually addressed C79.00 during that encounter — not just copy-forwarded from a problem list.
What This Code Means
C79.00 is the ICD-10-CM diagnosis code for secondary malignant neoplasm of unspecified kidney and renal pelvis. Cancer that has spread to an unspecified kidney or the renal pelvis (part of the kidney that collects urine) from a primary cancer elsewhere in the body. C79.00 sits in the ICD-10-CM chapter for neoplasms (c00-d49), within the section covering malignant neoplasms of ill-defined, other secondary and unspecified sites (c76-c80).
Under the CMS-HCC V28 risk adjustment model, C79.00 maps to Metastatic Cancer and Acute Leukemia (HCC 17) with a community, non-dual, aged base RAF weight of 0.368. Under the older V24 model, C79.00 mapped to the same category but with a base RAF weight of 2.484 — V28 recalibrated weights across the entire model. V28 is the CMS-HCC risk adjustment model that reached 100% phase-in for payment year 2026, replacing V24 which was used during the PY2024–PY2025 transition.
Use this code only when the specific kidney (right or left) cannot be determined from documentation. Because C79.00 maps to a payment HCC, the provider's documentation must satisfy MEAT criteria (Monitor, Evaluate, Assess, or Treat) for the encounter to count toward the patient's Medicare Advantage risk adjustment score. When documentation is ambiguous, coders should issue a provider query rather than assume the highest-specificity variant.
HCC Buddy maintains structured V28 and V24 mapping, RAF weights, and MEAT documentation criteria for C79.00 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
- •Use this code only when the specific kidney (right or left) cannot be determined from documentation
- •Always code the primary malignancy separately and confirm this is metastatic rather than primary kidney cancer
Clinical Significance
Secondary malignant neoplasm of unspecified kidney and renal pelvis indicates metastatic cancer has spread to the kidney without laterality documentation. Renal metastases can impair kidney function and may require nephrectomy or targeted therapy. The lack of laterality specification reduces clinical utility and should prompt a query.
Documentation Requirements
- ✓Primary cancer site documented and coded separately
- ✓Laterality — right or left kidney must be queried when not documented
- ✓Imaging confirmation (CT, MRI, ultrasound) of renal metastatic disease
- ✓Renal function assessment — creatinine, glomerular filtration rate
- ✓Whether the renal pelvis versus parenchyma is involved
Commonly Confused Codes
- •C79.01/C79.02 — Secondary malignant neoplasm of right/left kidney; use when laterality is documented
- •C64.1/C64.2/C64.9 — Primary malignant neoplasm of kidney; renal cell carcinoma is primary, not metastatic
- •C65.1/C65.2/C65.9 — Primary malignant neoplasm of renal pelvis; distinguish primary from secondary renal pelvis cancer
- •C79.10 — Secondary malignant neoplasm of unspecified urinary organs; kidney is a urinary organ but has its own specific codes