B59
BillablePneumocystosis
Last updated: FY2026 ICD-10-CM (Oct 1, 2025 – Sep 30, 2026) | CMS-HCC V28 (100% phase-in, PY2026)
Is B59 an HCC code?
Yes. B59 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 B59
For B59to 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 B59 during that encounter — not just copy-forwarded from a problem list.
What This Code Means
B59 is the ICD-10-CM diagnosis code for pneumocystosis. A serious lung infection caused by Pneumocystis, a fungal organism, that primarily affects people with weakened immune systems. B59 sits in the ICD-10-CM chapter for certain infectious and parasitic diseases (a00-b99), within the section covering protozoal diseases (b50-b64).
Under the CMS-HCC V28 risk adjustment model, B59 maps to Opportunistic Infections (HCC 6) with a community, non-dual, aged base RAF weight of 0.381. Under the older V24 model, B59 mapped to the same category but with a base RAF weight of 0.424 — 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.
This diagnosis is commonly associated with HIV/AIDS; verify and code the underlying immunocompromised condition. Because B59 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 B59 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
- •This diagnosis is commonly associated with HIV/AIDS; verify and code the underlying immunocompromised condition
- •Specify the type of pneumonia (PCP) and whether it is the initial diagnosis or recurrent
Clinical Significance
Pneumocystosis (Pneumocystis jirovecii pneumonia, formerly called PCP) is one of the most common and best-recognized AIDS-defining opportunistic infections. It remains the most frequent cause of respiratory failure in untreated HIV patients with CD4 counts below 200. Despite effective prophylaxis, it continues to occur in undiagnosed HIV patients and those non-adherent to treatment, carrying 10-20% mortality even with appropriate therapy.
Documentation Requirements
- ✓Bronchoalveolar lavage or induced sputum with positive Pneumocystis jirovecii stain (GMS, DFA, or PCR)
- ✓Chest imaging showing bilateral ground-glass opacities (classic pattern)
- ✓Arterial blood gas or pulse oximetry showing hypoxemia
- ✓CD4 count documented (typically <200 cells/microL) and HIV status
- ✓Treatment documented: trimethoprim-sulfamethoxazole for 21 days, adjunctive corticosteroids if PaO2 <70
- ✓LDH level (typically elevated; useful for prognostication)
Commonly Confused Codes
- •B58.3 (Pulmonary toxoplasmosis) - similar bilateral pneumonia in AIDS; bronchoalveolar lavage differentiates
- •J18.9 (Pneumonia, unspecified) - Pneumocystis pneumonia must be coded specifically with B59, not as unspecified pneumonia
- •B20 (HIV disease) - HIV should be coded in addition to B59, not instead of it
- •J15.9 (Unspecified bacterial pneumonia) - PCP is not bacterial; it is caused by a fungal organism