B46.9
BillableZygomycosis, unspecified
Last updated: FY2026 ICD-10-CM (Oct 1, 2025 – Sep 30, 2026) | CMS-HCC V28 (100% phase-in, PY2026)
Is B46.9 an HCC code?
Yes. B46.9 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 B46.9
For B46.9to 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 B46.9 during that encounter — not just copy-forwarded from a problem list.
What This Code Means
B46.9 is the ICD-10-CM diagnosis code for zygomycosis, unspecified. A fungal infection caused by zygomycete fungi when the specific type or location is not identified or documented. B46.9 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, B46.9 maps to Opportunistic Infections (HCC 6) with a community, non-dual, aged base RAF weight of 0.381. Under the older V24 model, B46.9 mapped to the same category but with a base RAF weight of 0.424 — 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 only when the specific zygomycosis type cannot be determined. Because B46.9 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 B46.9 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
- •Use only when the specific zygomycosis type cannot be determined
- •Request clarification from the provider regarding the fungal organism identified
Clinical Significance
Zygomycosis, unspecified, is the least specific code in the B46 category and should only be used when the specific zygomycete organism and site cannot be determined. Given that treatment differs between mucormycosis and other zygomycoses, and that site-specific management is critical, this code always warrants a provider query.
Documentation Requirements
- ✓At minimum, confirmed zygomycete infection via culture or histopathology
- ✓Provider query documented requesting organism identification and infection site
- ✓Immunocompromised status or other risk factors documented
- ✓Clinical presentation and affected anatomy recorded
- ✓Treatment plan documented