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B46.0 ICD-10-CM Code: Pulmonary mucormycosis

B46.0 maps to CMS-HCC V28 6. A source-labeled RAF reference is available. Documentation must support MEAT. MEAT criteria · RAF Calculator · free HCC coding tools

ICD-10-CM Code View

HCC Buddy Code Card

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FY 2026 Apr update / Certain infectious and parasitic diseases (A00-B99) / Mycoses (B35-B49)

B46.0

Billable / SpecificICD-10-CMOfficial ICD-10-CMCodebook guidance

Pulmonary mucormycosis

A serious fungal infection of the lungs caused by mucor fungi, typically occurring in immunocompromised patients and potentially spreading to other organs.

Buddy the Bee presenting code insight

Buddy Insight

Pulmonary mucormycosis is a rapidly progressive, life-threatening angioinvasive fungal infection with mortality rates exceeding 50%.

CMS-HCC V28

HCC 6

Code-level coefficient reference

CMS-HCC V24

Historical

Historical

Not used for CY2026 payment

ACA/HHS

HCC 006

Code-level coefficient reference

ESRD/PACE

HCC 6

Code-level coefficient reference

RXHCC

HCC 5

Code-level coefficient reference

Code Book Path

Official
B46Zygomycosis
B46.0Pulmonary mucormycosis

Inclusion Terms

Official

ICD-10-CM does not list inclusion terms for B46.0 in this effective period.

Excludes 2

Official

ICD-10-CM does not list Excludes 2 notes for B46.0 in this effective period.

Related Child Codes

Official
B46.1Rhinocerebral mucormycosis
B46.2Gastrointestinal mucormycosis
B46.3Cutaneous mucormycosis
B46.4Disseminated mucormycosis
B46.5Mucormycosis, unspecified

Includes

Official

ICD-10-CM does not list Includes notes for B46.0 in this effective period.

Excludes 1

Official

ICD-10-CM does not list Excludes 1 notes for B46.0 in this effective period.

Code First

Official

ICD-10-CM does not list Code First sequencing instructions for B46.0 in this effective period.

Use Additional

Official

ICD-10-CM does not list Use Additional Code instructions for B46.0 in this effective period.

Code Also

Official

ICD-10-CM does not list Code Also instructions for B46.0 in this effective period.

Buddy Documentation Tip

HCC Buddy guidance
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

MEAT Support

HCC Buddy guidance
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

Audit Caution

HCC Buddy guidance
Confusing mucormycosis with invasive aspergillosis — both are angioinvasive molds but have different histologic appearances and treatment protocols
Defaulting to unspecified mucormycosis (B46.5) when the pulmonary site is clearly documented
Not coding the underlying diabetic ketoacidosis or immunosuppressed state that predisposed to infection
Missing extension to contiguous structures (chest wall, mediastinum) that may require additional codes

Common Mistakes

HCC Buddy guidance
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

Current with CMS: FY2026 ICD-10-CM Apr 1 update (effective Apr 1 – Sep 30, 2026) · CMS-HCC V28, 100% phased in for payment year 2026. FY2027 code set already staged for October 1, 2026. How HCC Buddy stays current →

Is B46.0 an HCC code?

Yes. B46.0 (Pulmonary mucormycosis) maps to HCC 6, Opportunistic Infections under the CMS-HCC V28 risk adjustment model, with a source-labeled community non-dual aged reference coefficient of 0.381. Source-labeled code-level coefficients are references, not member totals. Actual contribution depends on complete member context, hierarchy and cleanup rules, interactions, and model year. HCC Buddy's RAF Calculator supports CMS-HCC V28 PY2026 and shows no score unless every required source and calculation check passes. It is billable for payment year 2026.

Coder answer: B46.0 is billable and maps to V28 HCC 6, Opportunistic Infections. Open it in the Code Book for the tabular path, RAF, and MEAT checklist.

Code
B46.0
Description
Pulmonary mucormycosis
HCC (V28)
HCC 6 — Opportunistic Infections
RAF reference coefficient
0.381
Billable
Yes
Payment year
2026

HCC Category Mapping

V28HCC 6, Opportunistic Infections
0.381
ESRDHCC 6, Opportunistic Infections
Not separately weighted
RxHCCHCC 5, Opportunistic Infections
Not separately weighted

These are source-labeled model coefficients, not member totals. A category may still be removed by hierarchy or model cleanup rules. Weights are not directly comparable across models: CMS-HCC V28 and V24 use Community, Non-Dual, Aged; ESRD uses the dialysis continuing-enrollee model; RxHCC is the Part D continuing-enrollee, non-low-income, aged weight (a larger scale than CMS-HCC). ACA/HHS has no single weight — it varies by metal level. Actual per-patient RAF contribution depends on member context, hierarchy and cleanup rules, interactions, and the model year used by the payer. V28 is the CMS-HCC model phased in over payment years 2024–2026; V24 remains available for historical review.

Work B46.0 in the Code Book — tabular path, V28 RAF reference, and MEAT checklist →

MEAT Criteria for B46.0

For B46.0 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 B46.0 during that encounter, not just copy-forwarded from a problem list.

Coder workflow notes

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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 source-labeled community, non-dual, aged reference coefficient of 0.381. No V24 mapping is shown for B46.0; use the applicable model and payment year when reviewing the V28 mapping. 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. Source-labeled code-level coefficients are references, not member totals. Actual contribution depends on complete member context, hierarchy and cleanup rules, interactions, and model year. HCC Buddy's RAF Calculator supports CMS-HCC V28 PY2026 and shows no score unless every required source and calculation check passes.

Document the site of infection and whether it is localized or disseminated. Because B46.0 maps to an HCC category, the provider's documentation must satisfy MEAT criteria (Monitor, Evaluate, Assess, or Treat) before the diagnosis is used for risk adjustment. 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, source-labeled coefficient references, 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

Child Codes

B46.0Pulmonary mucormycosis
HCC 6
B46.1Rhinocerebral mucormycosis
HCC 6
B46.2Gastrointestinal mucormycosis
HCC 6
B46.3Cutaneous mucormycosis
HCC 6
B46.4Disseminated mucormycosis
HCC 6
B46.5Mucormycosis, unspecified
HCC 6
B46.8Other zygomycoses
HCC 6
B46.9Zygomycosis, unspecified
HCC 6

Code Hierarchy

└B46Zygomycosis└B46.0Pulmonary mucormycosis
└B46.0Pulmonary mucormycosis

Because B46.0 maps to an HCC category, the documentation must satisfy MEAT criteria (Monitor, Evaluate, Assess, or Treat) before the diagnosis is used for risk adjustment.

B46.0 maps to CMS-HCC V28 category 6, Opportunistic Infections. See the ICD-10 to HCC mapping hub for how the V28 crosswalk works. The mapping identifies a payment HCC category for B46.0. Review its source-labeled HCC coefficient above, check the RAF Calculator with complete member context for CMS-HCC V28 PY2026, and confirm the documentation the chart needs before the code is submitted. HCC Buddy shows no RAF score unless every required source and calculation check passes.

Work B46.0 in HCC Buddy

Open B46.0 in the Code Book for the full Index-to-Tabular path, MEAT checklist, and V28 HCC mapping, or in the Encoder to code from a keyword search. Pro includes 7 days to try everything, no card required.

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