What is ICD-10 code B40.1?

B40.1 is the ICD-10-CM diagnosis code for Chronic pulmonary blastomycosis. A long-standing fungal lung infection caused by Blastomyces that develops gradually with persistent cough, chest pain, and progressive respiratory symptoms. It belongs to the ICD-10-CM chapter for certain infectious and parasitic diseases (a00-b99). B40.1 is a billable code, meaning it can be reported on a claim as a primary or secondary diagnosis when supported by documentation. B40.1 is part of the FY2026 ICD-10-CM code set published by the CMS National Center for Health Statistics and used on Medicare, Medicaid, and commercial claims in the United States.

Yes. B40.1 is a billable ICD-10-CM code that can be reported on professional and institutional claims as a primary or secondary diagnosis when the provider documentation supports the specific condition described. Billable codes in ICD-10-CM are coded to the highest level of specificity available for the documented diagnosis. B40.1 is current for fiscal year 2026 and remains in the active CMS ICD-10-CM code set published by the National Center for Health Statistics.

What is the V28 vs V24 difference for B40.1?

CMS phased in the V28 risk adjustment model over payment years 2024 (33%), 2025 (67%), and 2026 (100%), replacing V24. V28 consolidates HCC categories, removes some lower-acuity conditions, and recalibrates RAF weights across the entire model. B40.1 was a payment HCC under V24 (Pneumococcal Pneumonia, Empyema, Lung Abscess) but the V28 recalibration removed it from the risk adjustment model. Both models can still appear in legacy data and in payer-specific lookback periods.

What should coders know when reporting B40.1?

Chronic form often mimics tuberculosis or lung cancer; review imaging findings and clinical course carefully Ensure documentation clearly indicates chronic progression over weeks to months Because B40.1 maps to a payment HCC, the documentation must also satisfy MEAT criteria (Monitor, Evaluate, Assess, or Treat) for the encounter to count toward the patient's risk adjustment score.

2026 ICD-10-CM B40.1: Chronic pulmonary

ICD-10-CM Code View

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Code lookupB40.1Effective periodFY2026 Apr Update (Apr 1-Sep 30)

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

B40.1

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

Chronic pulmonary blastomycosis

A long-standing fungal lung infection caused by Blastomyces that develops gradually with persistent cough, chest pain, and progressive respiratory symptoms.

Buddy Insight

Chronic pulmonary blastomycosis presents as a progressive fibrocavitary lung disease that mimics tuberculosis and lung cancer.

CMS-HCC V28

N/A

—

Not risk-adjusted for this model/period.

Not mapped

CMS-HCC V24

Mapped

HCC 115

Pneumococcal Pneumonia, Empye...

RAF 0.130

ACA/HHS

Mapped

HCC 163

HHS-HCC 163

Varies by metal level

ESRD/PACE

Mapped

HCC 115

Pneumococcal Pneumonia, Empye...

RAF 0.030

RXHCC

N/A

—

Not risk-adjusted for this model/period.

Not mapped

Code Book Path

Official

B40Blastomycosis

B40.1Chronic pulmonary blastomycosis

Inclusion Terms

Official

ICD-10-CM does not list inclusion terms for B40.1 in this effective period.

Excludes 2

Official

ICD-10-CM does not list Excludes 2 notes for B40.1 in this effective period.

Related Child Codes

Official

B40.0Acute pulmonary blastomycosis

B40.2Pulmonary blastomycosis, unspecified

B40.3Cutaneous blastomycosis

B40.7Disseminated blastomycosis

B40.8Other forms of blastomycosis

Includes

Official

ICD-10-CM does not list Includes notes for B40.1 in this effective period.

Excludes 1

Official

Brazilian blastomycosis (B41.-)
keloidal blastomycosis (B48.0)

Code First

Official

ICD-10-CM does not list Code First sequencing instructions for B40.1 in this effective period.

Use Additional

Official

ICD-10-CM does not list Use Additional Code instructions for B40.1 in this effective period.

Code Also

Official

ICD-10-CM does not list Code Also instructions for B40.1 in this effective period.

Buddy Documentation Tip

HCC Buddy guidance

Documented chronic/progressive course over weeks to months

Imaging showing mass lesions, fibronodular disease, or cavitary changes

Positive Blastomyces culture, antigen, or histopathology from respiratory specimens

Exclusion of tuberculosis and malignancy documented in the record

MEAT Support

HCC Buddy guidance

Documented chronic/progressive course over weeks to months

Imaging showing mass lesions, fibronodular disease, or cavitary changes

Positive Blastomyces culture, antigen, or histopathology from respiratory specimens

Exclusion of tuberculosis and malignancy documented in the record

Audit Caution

HCC Buddy guidance

Coding as suspected lung cancer when the mass lesion is actually chronic blastomycosis — always wait for pathology confirmation

Using the unspecified B40.2 code when documentation clearly supports a chronic progressive course

Not capturing skin or bone involvement that may coexist with chronic pulmonary disease

Common Mistakes

HCC Buddy guidance

B40.0 (Acute pulmonary blastomycosis) - acute form has rapid onset with pneumonic infiltrates; chronic shows progressive fibrocavitary disease

A15.0 (Tuberculosis of lung) - blastomycosis can be radiographically identical to TB; microbiologic studies differentiate

C34.90 (Malignant neoplasm of unspecified part of bronchus or lung) - mass-like blastomycosis can be confused with lung cancer until biopsy confirms fungal etiology

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 B40.1 an HCC code?

Yes. B40.1 maps to Pneumococcal Pneumonia, Empyema, Lung Abscess under the V24 model but is not retained in V28.

Code: B40.1
Description: Chronic pulmonary blastomycosis
HCC (V28): No CMS-HCC V28 mapping
RAF: —
Billable: Yes
Payment year: 2026

HCC Category Mapping

V24HCC 115, Pneumococcal Pneumonia, Empyema, Lung Abscess

0.130

ESRDHCC 115, Pneumococcal Pneumonia, Empyema, Lung Abscess

0.030

Each model's RAF is its CMS base weight for that model's standard population, so 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 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.

Work B40.1 in the Code Book — tabular path, V28 RAF, and MEAT checklist →

MEAT Criteria for B40.1

For B40.1to 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 B40.1 during that encounter, not just copy-forwarded from a problem list.

Coder workflow notes

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What This Code Means

B40.1 is the ICD-10-CM diagnosis code for chronic pulmonary blastomycosis. A long-standing fungal lung infection caused by Blastomyces that develops gradually with persistent cough, chest pain, and progressive respiratory symptoms. B40.1 sits in the ICD-10-CM chapter for certain infectious and parasitic diseases (a00-b99), within the section covering mycoses (b35-b49).

Under the older CMS-HCC V24 model, B40.1 maps to Pneumococcal Pneumonia, Empyema, Lung Abscess (HCC 115) with a community, non-dual, aged base RAF weight of 0.130. 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.

Chronic form often mimics tuberculosis or lung cancer; review imaging findings and clinical course carefully. Because B40.1 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 B40.1 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.

Coding Tips

•Chronic form often mimics tuberculosis or lung cancer; review imaging findings and clinical course carefully
•Ensure documentation clearly indicates chronic progression over weeks to months

Clinical Significance

Chronic pulmonary blastomycosis presents as a progressive fibrocavitary lung disease that mimics tuberculosis and lung cancer. Long-term antifungal therapy is typically required, and the chronic nature indicates ongoing disease burden and resource utilization that risk adjustment models need to capture accurately.

Documentation Requirements

✓Documented chronic/progressive course over weeks to months
✓Imaging showing mass lesions, fibronodular disease, or cavitary changes
✓Positive Blastomyces culture, antigen, or histopathology from respiratory specimens
✓Exclusion of tuberculosis and malignancy documented in the record
✓Ongoing antifungal treatment plan documented

Commonly Confused Codes

•B40.0 (Acute pulmonary blastomycosis) - acute form has rapid onset with pneumonic infiltrates; chronic shows progressive fibrocavitary disease
•A15.0 (Tuberculosis of lung) - blastomycosis can be radiographically identical to TB; microbiologic studies differentiate
•C34.90 (Malignant neoplasm of unspecified part of bronchus or lung) - mass-like blastomycosis can be confused with lung cancer until biopsy confirms fungal etiology