HCC Buddy Code Card
Digital ICD-10 code-book layout with official code detail, always-visible risk models, Code Trumping, and Buddy coding guidance.
FY 2026 Apr update / Certain infectious and parasitic diseases (A00-B99) / Mycoses (B35-B49)
B46.0
Billable / SpecificICD-10-CMOfficial ICD-10-CMCodebook guidancePulmonary mucormycosis
A serious fungal infection of the lungs caused by mucor fungi, typically occurring in immunocompromised patients and potentially spreading to other organs.
Buddy Insight
Pulmonary mucormycosis is a rapidly progressive, life-threatening angioinvasive fungal infection with mortality rates exceeding 50%.
CMS-HCC V28
MappedHCC 6
RAF 0.439
CMS-HCC V24
MappedHCC 6
RAF 0.440
ACA/HHS
00
RAF 0
ESRD/PACE
MappedHCC 6
RAF 0.0
RXHCC
MappedHCC 5
RAF 0.0
Code Trumping
Basket needed
Code Book Path
Inclusion Terms
OfficialICD-10-CM does not list inclusion terms for B46.0 in this effective period.
Excludes 2
OfficialICD-10-CM does not list Excludes 2 notes for B46.0 in this effective period.
Related Child Codes
Includes
OfficialICD-10-CM does not list Includes notes for B46.0 in this effective period.
Excludes 1
OfficialICD-10-CM does not list Excludes 1 notes for B46.0 in this effective period.
Code First
OfficialICD-10-CM does not list Code First sequencing instructions for B46.0 in this effective period.
Use Additional
OfficialICD-10-CM does not list Use Additional Code instructions for B46.0 in this effective period.
Code Also
OfficialICD-10-CM does not list Code Also instructions for B46.0 in this effective period.
Buddy Documentation Tip
MEAT Support
Audit Caution
Common Mistakes
Last updated: FY2026 ICD-10-CM Apr update, Apr 1, 2026 through Sep 30, 2026. CMS-HCC V28 is 100% phased in for payment year 2026.
Is B46.0 an HCC code?
Yes. B46.0 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 B46.0
For B46.0to 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 B46.0 during that encounter — not just copy-forwarded from a problem list.
What This Code Means
B46.0 is the ICD-10-CM diagnosis code for pulmonary mucormycosis. A serious fungal infection of the lungs caused by mucor fungi, typically occurring in immunocompromised patients and potentially spreading to other organs. B46.0 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, B46.0 maps to Opportunistic Infections (HCC 6) with a community, non-dual, aged base RAF weight of 0.439. Under the older V24 model, B46.0 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.
Document the site of infection and whether it is localized or disseminated. Because B46.0 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 B46.0 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
- •Document the site of infection and whether it is localized or disseminated
- •Verify immunocompromised status (diabetes, transplant, chemotherapy) as this is a key risk factor
Clinical Significance
Pulmonary mucormycosis is a rapidly progressive, life-threatening angioinvasive fungal infection with mortality rates exceeding 50%. It most commonly affects patients with uncontrolled diabetes mellitus (especially diabetic ketoacidosis), hematologic malignancies, and organ transplant recipients. Early diagnosis and aggressive treatment with combined surgical and antifungal therapy are essential.
Documentation Requirements
- ✓Tissue biopsy showing broad, ribbon-like, non-septate hyphae with right-angle branching
- ✓Culture confirmation of Mucorales species when possible (cultures often negative)
- ✓CT imaging with reverse halo sign, pleural effusion, or cavitation
- ✓Underlying risk factor documented: diabetic ketoacidosis, neutropenia, transplant, iron overload
- ✓Treatment documented: surgical debridement and amphotericin B therapy
Commonly Confused Codes
- •B44.0 (Invasive pulmonary aspergillosis) - most common diagnostic confusion; aspergillus shows septate, acute-angle hyphae vs mucor's non-septate, right-angle hyphae
- •B46.4 (Disseminated mucormycosis) - use when infection has spread beyond the lungs
- •B46.5 (Mucormycosis, unspecified) - do not use when pulmonary site is documented