B46.1 ICD-10-CM Code: Rhinocerebral mucormycosis
B46.1 maps to CMS-HCC V28 6. A source-labeled RAF reference is available. Confirm the documented diagnosis and applicable coding requirements. MEAT criteria · RAF Calculator · HCC Buddy coding tools
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FY 2026 Apr update / Certain infectious and parasitic diseases (A00-B99) / Mycoses (B35-B49)
B46.1
Billable / SpecificICD-10-CMOfficial ICD-10-CMCodebook guidanceRhinocerebral mucormycosis
A serious fungal infection caused by mucormycosis that affects the nasal passages and spreads to the brain and surrounding tissues. This is a life-threatening condition that typically occurs in people with weakened immune systems.
Buddy Insight
Rhinocerebral mucormycosis is the most common and most recognizable form of mucormycosis, originating in the sinuses and rapidly invading through bone into the orbit and brain.
CMS-HCC V28
MappedHCC 6
Coefficient HCC 6: 0.381 (Community Non-Dual Aged (CNA))
CMS-HCC V24
HistoricalHistorical
Not used for CY2026 payment
ACA/HHS
MappedHCC 006
Code-level coefficient reference
ESRD/PACE
MappedHCC 6
Code-level coefficient reference
RXHCC
MappedHCC 5
Code-level coefficient reference
Code Book Path
Inclusion Terms
OfficialNo inclusion terms are included in this display for B46.1. Check the code and parent instructions in the Code Book.
Excludes 2
Official- carrier or suspected carrier of infectious disease (Z22.-)Inherited from A00-B99, B35-B49
- infectious and parasitic diseases complicating pregnancy, childbirth and the puerperium (O98.-)Inherited from A00-B99, B35-B49
- infectious and parasitic diseases specific to the perinatal period (P35-P39)Inherited from A00-B99, B35-B49
- influenza and other acute respiratory infections (J00-J22)Inherited from A00-B99, B35-B49
- hypersensitivity pneumonitis due to organic dust (J67.-)Inherited from A00-B99, B35-B49
- mycosis fungoides (C84.0-)Inherited from A00-B99, B35-B49
Related Codes
Includes
Official- diseases generally recognized as communicable or transmissibleInherited from A00-B99
Excludes 1
Official- certain localized infections - see body system-related chaptersInherited from A00-B99
Code First
OfficialNo Code First sequencing instructions are included in this display for B46.1. Check the code and parent instructions in the Code Book.
Use Additional
Official- code to identify resistance to antimicrobial drugs (Z16.-)Inherited from A00-B99
Code Also
OfficialNo Code Also instructions are included in this display for B46.1. Check the code and parent instructions in the Code Book.
Buddy Documentation Tip
MEAT Support
Audit Caution
Common Mistakes
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 B46.1 an HCC code?
Yes. B46.1 (Rhinocerebral 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: B46.1 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
- B46.1
- Description
- Rhinocerebral mucormycosis
- HCC (V28)
- HCC 6 — Opportunistic Infections
- RAF reference coefficient
- 0.381
- Billable
- Yes
- Payment year
- 2026
HCC Category Mapping
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 B46.1 in the Code Book — tabular path, V28 RAF reference, and MEAT checklist →
MEAT review for B46.1
For B46.1, confirm that the documentation supports the diagnosis and meets the applicable coding, encounter, program and payer requirements. MEAT (Monitor, Evaluate, Assess, or Treat) is a review mnemonic, not a universal CMS coding rule.
- 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
Coder workflow notes
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What This Code Means
B46.1 is the ICD-10-CM diagnosis code for rhinocerebral mucormycosis. A serious fungal infection caused by mucormycosis that affects the nasal passages and spreads to the brain and surrounding tissues. This is a life-threatening condition that typically occurs in people with weakened immune systems. B46.1 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, B46.1 maps to Opportunistic Infections (HCC 6) with a source-labeled community, non-dual, aged reference coefficient of 0.381. For CY2026 non-PACE Medicare Advantage, CMS uses 100% of the 2024 CMS-HCC model (V28). PACE uses a separate model blend. 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.
Rhinocerebral mucormycosis is a specific site specification of mucormycosis - do not use the more general B46.9 code if the rhinocerebral location is documented. For B46.1, confirm that the documentation supports the diagnosis and meets the applicable coding, encounter, program and payer requirements. MEAT (Monitor, Evaluate, Assess, or Treat) is a review mnemonic, not a universal CMS coding rule. 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 B46.1 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
- •Rhinocerebral mucormycosis is a specific site specification of mucormycosis - do not use the more general B46.9 code if the rhinocerebral location is documented
- •This code often requires additional documentation of the underlying immunocompromised state (such as diabetes, HIV, or hematologic malignancy) which should be coded separately to capture the complete clinical picture
Clinical Significance
Rhinocerebral mucormycosis is the most common and most recognizable form of mucormycosis, originating in the sinuses and rapidly invading through bone into the orbit and brain. It is strongly associated with diabetic ketoacidosis and carries mortality rates of 25-60%. The angioinvasive nature causes tissue necrosis, black eschar formation, and rapid progression requiring emergent surgical intervention.
Documentation Requirements
- ✓CT/MRI imaging showing sinus opacification with bone erosion and orbital/intracranial extension
- ✓Tissue biopsy from nasal/sinus debridement confirming Mucorales
- ✓Clinical findings: facial pain, nasal congestion, black necrotic eschar, cranial nerve palsies, proptosis
- ✓Underlying condition: diabetic ketoacidosis, blood glucose levels, hemoglobin A1c
- ✓Surgical debridement performed and extent documented
Commonly Confused Codes
- •B46.0 (Pulmonary mucormycosis) - lung involvement only; rhinocerebral involves sinuses, orbit, and brain
- •J32.9 (Chronic sinusitis, unspecified) - invasive fungal sinusitis is a surgical emergency, not chronic bacterial sinusitis
- •B46.5 (Mucormycosis, unspecified) - never use when rhinocerebral presentation is documented