A42.0 ICD-10-CM Code: Pulmonary actinomycosis
A42.0 is not a CMS-HCC payment code. MEAT criteria · RAF Calculator · HCC Buddy coding tools
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FY 2026 Apr update / Certain infectious and parasitic diseases (A00-B99) / Other bacterial diseases (A30-A49)
A42.0
Billable / SpecificICD-10-CMOfficial ICD-10-CMCodebook guidancePulmonary actinomycosis
Pulmonary actinomycosis is a chronic bacterial infection of the lungs caused by Actinomyces bacteria, which are normally found in the mouth and can cause slow-growing infections with abscess formation. This condition typically develops after aspiration or trauma and presents with persistent cough, fever, and chest symptoms.
Buddy Insight
Pulmonary actinomycosis is a chronic bacterial lung infection caused by Actinomyces species (typically A.
CMS-HCC V28
N/A—
Not mapped
CMS-HCC V24
HistoricalHistorical
Not used for CY2026 payment
ACA/HHS
N/A—
Not mapped
ESRD/PACE
MappedHCC 115
Code-level coefficient reference
RXHCC
N/A—
Not mapped
Code Book Path
Inclusion Terms
OfficialNo inclusion terms are included in this display for A42.0. 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
- infectious and parasitic diseases complicating pregnancy, childbirth and the puerperium (O98.-)Inherited from A00-B99
- infectious and parasitic diseases specific to the perinatal period (P35-P39)Inherited from A00-B99
- influenza and other acute respiratory infections (J00-J22)Inherited from A00-B99
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, A42
- actinomycetoma (B47.1)Inherited from A00-B99, A42
Code First
OfficialNo Code First sequencing instructions are included in this display for A42.0. 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 A42.0. 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 A42.0 an HCC code?
A42.0 is not in the CMS-HCC V28 or V24 community payment model. A42.0 has a separate mapping under the CMS-HCC ESRD model (HCC 115 (Pneumococcal Pneumonia/Empyema/Lung Abscess)); the applicable result needs member context.
- Code
- A42.0
- Description
- Pulmonary actinomycosis
- HCC (V28)
- No CMS-HCC V28 mapping
- RAF reference coefficient
- —
- 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 A42.0 in the Code Book — tabular path, V28 RAF reference, and MEAT checklist →
MEAT review for A42.0
For A42.0, 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
A42.0 is the ICD-10-CM diagnosis code for pulmonary actinomycosis. Pulmonary actinomycosis is a chronic bacterial infection of the lungs caused by Actinomyces bacteria, which are normally found in the mouth and can cause slow-growing infections with abscess formation. This condition typically develops after aspiration or trauma and presents with persistent cough, fever, and chest symptoms. A42.0 sits in the ICD-10-CM chapter for certain infectious and parasitic diseases (a00-b99), within the section covering other bacterial diseases (a30-a49).
A42.0 has no mapping under the CMS-HCC V28 or V24 community payment models. A42.0 has a separate mapping under the CMS-HCC ESRD model (HCC 115 (Pneumococcal Pneumonia/Empyema/Lung Abscess)); the applicable result needs member context. Do not assign V28 risk adjustment value from this page; verify the applicable model and payment year before using this code for risk adjustment.
Actinomycosis is often misdiagnosed as tuberculosis or malignancy; verify the diagnosis is confirmed by culture or histopathology before coding.
HCC Buddy maintains structured V28 and V24 mapping, source-labeled coefficient references, and MEAT documentation criteria for A42.0 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
- •Actinomycosis is often misdiagnosed as tuberculosis or malignancy; verify the diagnosis is confirmed by culture or histopathology before coding
- •This code is specific to pulmonary involvement; if the infection affects other sites (cervicofacial, abdominal, CNS), use the appropriate A42 subcode instead
Clinical Significance
Pulmonary actinomycosis is a chronic bacterial lung infection caused by Actinomyces species (typically A. israelii), an anaerobic filamentous bacterium. It characteristically crosses tissue planes and can form draining sinus tracts. Often mimics lung cancer or tuberculosis on imaging, leading to diagnostic delay. Requires prolonged antibiotic therapy (6-12 months of penicillin or amoxicillin).
Documentation Requirements
- ✓Culture or histopathologic identification of Actinomyces species from pulmonary specimen
- ✓Characteristic sulfur granules on pathology if biopsy performed
- ✓Chest imaging showing consolidation, mass lesion, or cavitary disease (often mimics malignancy)
- ✓Clinical presentation (chronic cough, weight loss, hemoptysis, chest wall sinus tract)
- ✓Extended antibiotic treatment plan documented (typically 6-12 months)
Commonly Confused Codes
- •A43.0 (Pulmonary nocardiosis): Nocardia is aerobic and partially acid-fast; Actinomyces is anaerobic and non-acid-fast: different organisms requiring different treatment
- •C34.90 (Malignant neoplasm of lung): Pulmonary actinomycosis commonly mimics lung cancer on imaging; tissue diagnosis is essential for differentiation
- •A15.0 (Tuberculosis of lung): TB and actinomycosis can have similar radiographic presentations but are different infections