A43.0 ICD-10-CM Code: Pulmonary nocardiosis
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) / Other bacterial diseases (A30-A49)
A43.0
Billable / SpecificICD-10-CMOfficial ICD-10-CMCodebook guidancePulmonary nocardiosis
A lung infection caused by Nocardia bacteria, which can cause cough, chest pain, and difficulty breathing. This is a serious infection that typically occurs in people with weakened immune systems.
Buddy Insight
Pulmonary nocardiosis is a serious lung infection caused by Nocardia species (typically N.
CMS-HCC V28
00
RAF 0
CMS-HCC V24
MappedHCC 115
RAF 0.339
ACA/HHS
00
RAF 0
ESRD/PACE
MappedHCC 115
RAF 0.0
RXHCC
00
RAF 0
Code Trumping
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Code Book Path
Inclusion Terms
OfficialICD-10-CM does not list inclusion terms for A43.0 in this effective period.
Excludes 2
OfficialICD-10-CM does not list Excludes 2 notes for A43.0 in this effective period.
Related Child Codes
Includes
OfficialICD-10-CM does not list Includes notes for A43.0 in this effective period.
Excludes 1
OfficialICD-10-CM does not list Excludes 1 notes for A43.0 in this effective period.
Code First
OfficialICD-10-CM does not list Code First sequencing instructions for A43.0 in this effective period.
Use Additional
OfficialICD-10-CM does not list Use Additional Code instructions for A43.0 in this effective period.
Code Also
OfficialICD-10-CM does not list Code Also instructions for A43.0 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 A43.0 an HCC code?
Yes. A43.0 maps to Pneumococcal Pneumonia, Empyema, Lung Abscess under the V24 model but is not retained in V28.
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 A43.0
For A43.0to 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 A43.0 during that encounter, not just copy-forwarded from a problem list.
What This Code Means
A43.0 is the ICD-10-CM diagnosis code for pulmonary nocardiosis. A lung infection caused by Nocardia bacteria, which can cause cough, chest pain, and difficulty breathing. This is a serious infection that typically occurs in people with weakened immune systems. A43.0 sits in the ICD-10-CM chapter for certain infectious and parasitic diseases (a00-b99), within the section covering other bacterial diseases (a30-a49).
Under the older CMS-HCC V24 model, A43.0 maps to Pneumococcal Pneumonia, Empyema, Lung Abscess (HCC 115) with a community, non-dual, aged base RAF weight of 0.339. 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.
Verify the infection site is specifically the lungs/pulmonary system; other Nocardia infections have different codes (A43.1 for cutaneous, A43.8 for other sites). Because A43.0 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 A43.0 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
- •Verify the infection site is specifically the lungs/pulmonary system; other Nocardia infections have different codes (A43.1 for cutaneous, A43.8 for other sites)
- •Document the causative organism as Nocardia species in the medical record to support accurate coding and ensure appropriate antibiotic therapy documentation
Clinical Significance
Pulmonary nocardiosis is a serious lung infection caused by Nocardia species (typically N. asteroides complex), an aerobic, partially acid-fast filamentous bacterium. It predominantly affects immunocompromised patients (organ transplant recipients, those on chronic corticosteroids, HIV/AIDS) and can disseminate to the brain and skin. Requires prolonged treatment with trimethoprim-sulfamethoxazole (often 6-12 months).
Documentation Requirements
- ✓Culture of Nocardia species from respiratory specimens (sputum, bronchoalveolar lavage, or lung biopsy)
- ✓Nocardia species identification (different species have different antibiotic susceptibility patterns)
- ✓Chest imaging showing nodules, cavities, consolidation, or pleural effusion
- ✓Immunocompromised status documented (transplant, HIV, chronic steroids, malignancy)
- ✓Brain imaging (MRI) to evaluate for CNS dissemination, which occurs in up to 44% of pulmonary cases
Commonly Confused Codes
- •A42.0 (Pulmonary actinomycosis): Actinomyces is anaerobic and non-acid-fast; Nocardia is aerobic and partially acid-fast: requires different antibiotics
- •A15.0 (Tuberculosis of lung): Both are partially acid-fast, but Nocardia is filamentous on gram stain; AFB smear and culture differentiate them
- •B44.1 (Other pulmonary aspergillosis): Both affect immunocompromised patients with similar imaging findings; culture and pathology differentiate