B46.4
BillableDisseminated mucormycosis
Last updated: FY2026 ICD-10-CM (Oct 1, 2025 – Sep 30, 2026) | CMS-HCC V28 (100% phase-in, PY2026)
Is B46.4 an HCC code?
Yes. B46.4 maps to Opportunistic Infections under the CMS-HCC V28 risk adjustment model (and Opportunistic Infections 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 B46.4
For B46.4to 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 B46.4 during that encounter — not just copy-forwarded from a problem list.
What This Code Means
B46.4 is the ICD-10-CM diagnosis code for disseminated mucormycosis. A serious systemic fungal infection where mucormycosis has spread throughout the body affecting multiple organ systems. B46.4 sits in the ICD-10-CM chapter for certain infectious and parasitic diseases (a00-b99), within the section covering mycoses (b35-b49).
Under the CMS-HCC V28 risk adjustment model, B46.4 maps to Opportunistic Infections (HCC 6) with a community, non-dual, aged base RAF weight of 0.439. Under the older V24 model, B46.4 mapped to the same category but with a base RAF weight of 0.440 — 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.
Identify and code all affected body systems separately when documented. Because B46.4 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 B46.4 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
- •Identify and code all affected body systems separately when documented
- •This code indicates advanced disease; document underlying immunocompromised conditions
Clinical Significance
Disseminated mucormycosis represents hematogenous spread of Mucorales to multiple organ systems and carries the highest mortality rate of any mucormycosis form (exceeding 90%). It most commonly affects patients with profound neutropenia, hematologic malignancies, or deferoxamine therapy for iron overload. This code reflects the most severe end of the mucormycosis spectrum.
Documentation Requirements
- ✓Tissue confirmation of Mucorales from two or more non-contiguous sites
- ✓All affected organ systems specifically identified and documented
- ✓Blood culture results (positive Mucorales fungemia if present)
- ✓Profound immunosuppression documented: absolute neutrophil count, chemotherapy regimen, transplant status
- ✓Multi-modal treatment documented: surgical debridement of accessible sites plus systemic amphotericin B