C91.00
BillableAcute lymphoblastic leukemia not having achieved remission
Last updated: FY2026 ICD-10-CM (Oct 1, 2025 – Sep 30, 2026) | CMS-HCC V28 (100% phase-in, PY2026)
Is C91.00 an HCC code?
Yes. C91.00 maps to Metastatic Cancer to Peritoneum and Other Specified Sites 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 C91.00
For C91.00 to 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 C91.00 during that encounter — not just copy-forwarded from a problem list.
What This Code Means
C91.00 is the ICD-10-CM diagnosis code for acute lymphoblastic leukemia not having achieved remission. A fast-growing blood cancer affecting young white blood cells that has not responded to treatment or achieved remission. C91.00 sits in the ICD-10-CM chapter for neoplasms (c00-d49), within the section covering malignant neoplasms of lymphoid, hematopoietic and related tissue (c81-c96).
Under the CMS-HCC V28 risk adjustment model, C91.00 maps to Metastatic Cancer to Peritoneum and Other Specified Sites (HCC 18) with a community, non-dual, aged base RAF weight of 0.368. Under the older CMS-HCC V24 model, C91.00 maps to Metastatic Cancer and Acute Leukemia (HCC 8) with a community, non-dual, aged base RAF weight of 2.484. 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.
Acute lymphoblastic leukemia (ALL) is primarily a pediatric cancer; note patient age in documentation. Because C91.00 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 C91.00 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
- •Acute lymphoblastic leukemia (ALL) is primarily a pediatric cancer; note patient age in documentation
- •Remission status must be explicitly documented; do not assume based on treatment alone
Clinical Significance
Acute lymphoblastic leukemia (ALL) is a rapidly progressive malignancy of lymphoid precursor cells that infiltrates the bone marrow, peripheral blood, and potentially the central nervous system and other organs. While predominantly a pediatric disease, adult ALL carries a worse prognosis. Non-remission status indicates the disease is refractory to initial induction therapy, which is associated with very poor outcomes requiring alternative treatment strategies.
Documentation Requirements
- ✓Documentation must include bone marrow biopsy with blast percentage, immunophenotyping (B-cell versus T-cell lineage), cytogenetic and molecular studies (particularly Philadelphia chromosome status), cerebrospinal fluid analysis, treatment protocol, response assessment, and explicit non-remission status.
- ✓Risk stratification must be recorded.
Commonly Confused Codes
- •C91.01 (ALL in remission) requires documented remission with blast clearance.
- •C91.02 (ALL in relapse) requires prior remission followed by recurrence.
- •C91.10 (chronic lymphocytic leukemia) is an indolent disease affecting mature lymphocytes.
- •C83.x (diffuse B-cell lymphoma) involves solid tumor presentations rather than leukemic.