A31.0
BillablePulmonary mycobacterial infection
Last updated: FY2026 ICD-10-CM (Oct 1, 2025 – Sep 30, 2026) | CMS-HCC V28 (100% phase-in, PY2026)
Is A31.0 an HCC code?
Yes. A31.0 maps to Opportunistic Infections under the CMS-HCC V28 risk adjustment model (and Opportunistic Infections under V24).
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 A31.0
For A31.0 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 A31.0 during that encounter — not just copy-forwarded from a problem list.
What This Code Means
A31.0 is the ICD-10-CM diagnosis code for pulmonary mycobacterial infection. This is a bacterial lung infection caused by mycobacteria (a type of bacteria), which is different from the more common tuberculosis. It affects the lungs and respiratory system, causing symptoms like cough and breathing difficulties. A31.0 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 CMS-HCC V28 risk adjustment model, A31.0 maps to Opportunistic Infections (HCC 6) with a community, non-dual, aged base RAF weight of 0.439. Under the older V24 model, A31.0 mapped to the same category but with a base RAF weight of 0.440 — V28 recalibrated weights across the entire model. 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 specific type of mycobacterial infection (such as MAC - Mycobacterium avium complex) as this may require additional specificity codes. Because A31.0 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 A31.0 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
- •Verify the specific type of mycobacterial infection (such as MAC - Mycobacterium avium complex) as this may require additional specificity codes
- •Confirm whether this is a primary infection or a secondary/opportunistic infection, particularly in immunocompromised patients, as this may affect coding accuracy
Clinical Significance
Pulmonary mycobacterial infection (nontuberculous mycobacteria, or NTM) is a chronic progressive lung disease most commonly caused by Mycobacterium avium complex (MAC) or M. abscessus. It predominantly affects elderly women with bronchiectasis (Lady Windermere syndrome) and immunocompromised patients, requiring prolonged multi-drug treatment regimens often lasting 12-18 months.
Documentation Requirements
- ✓Sputum cultures identifying specific NTM species (at least 2 positive sputum cultures, or 1 positive bronchial wash/BAL)
- ✓CT chest showing nodular bronchiectatic or cavitary disease pattern
- ✓Clinical symptoms consistent with pulmonary NTM (chronic cough, fatigue, weight loss)
- ✓Exclusion of other diagnoses, particularly pulmonary tuberculosis
- ✓ATS/IDSA diagnostic criteria met: clinical, radiographic, and microbiologic criteria all fulfilled