B59 ICD-10-CM Code: Pneumocystosis
B59 maps to CMS-HCC V28 6. A source-labeled RAF reference is available. Confirm the documented diagnosis and applicable coding requirements. MEAT criteria · RAF Calculator · HCC Buddy coding tools
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FY 2026 Apr update / Certain infectious and parasitic diseases (A00-B99) / Protozoal diseases (B50-B64)
B59
Billable / SpecificICD-10-CMOfficial ICD-10-CMCodebook guidancePneumocystosis
A serious lung infection caused by Pneumocystis, a fungal organism, that primarily affects people with weakened immune systems.
Buddy Insight
Pneumocystosis (Pneumocystis jirovecii pneumonia, formerly called PCP) is one of the most common and best-recognized AIDS-defining opportunistic infections.
CMS-HCC V28
MappedHCC 6
Coefficient HCC 6: 0.381 (Community Non-Dual Aged (CNA))
CMS-HCC V24
HistoricalHistorical
Not used for CY2026 payment
ACA/HHS
MappedHCC 006
Code-level coefficient reference
ESRD/PACE
MappedHCC 6
Code-level coefficient reference
RXHCC
MappedHCC 5
Code-level coefficient reference
Code Book Path
Inclusion Terms
Official- Pneumonia due to Pneumocystis carinii
- Pneumonia due to Pneumocystis jirovecii
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
No related codes are included in this display for B59. Check the Code Book for the complete code path.
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, B50-B64
- amebiasis (A06.-)Inherited from A00-B99, B50-B64
- other protozoal intestinal diseases (A07.-)Inherited from A00-B99, B50-B64
Code First
OfficialNo Code First sequencing instructions are included in this display for B59. 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 B59. 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 B59 an HCC code?
Yes. B59 (Pneumocystosis) maps to HCC 6, Opportunistic Infections under the CMS-HCC V28 risk adjustment model, with a source-labeled community non-dual aged reference coefficient of 0.381. Source-labeled code-level coefficients are references, not member totals. Actual contribution depends on complete member context, hierarchy and cleanup rules, interactions, and model year. HCC Buddy's RAF Calculator supports CMS-HCC V28 PY2026 and shows no score unless every required source and calculation check passes. It is billable for payment year 2026.
Coder answer: B59 is billable and maps to V28 HCC 6, Opportunistic Infections. Open it in the Code Book for the tabular path, RAF, and MEAT checklist.
- Code
- B59
- Description
- Pneumocystosis
- HCC (V28)
- HCC 6 — Opportunistic Infections
- RAF reference coefficient
- 0.381
- 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 B59 in the Code Book — tabular path, V28 RAF reference, and MEAT checklist →
MEAT review for B59
For B59, 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
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 source-labeled community, non-dual, aged reference coefficient of 0.381. For CY2026 non-PACE Medicare Advantage, CMS uses 100% of the 2024 CMS-HCC model (V28). PACE uses a separate model blend. Source-labeled code-level coefficients are references, not member totals. Actual contribution depends on complete member context, hierarchy and cleanup rules, interactions, and model year. HCC Buddy's RAF Calculator supports CMS-HCC V28 PY2026 and shows no score unless every required source and calculation check passes.
This diagnosis is commonly associated with HIV/AIDS; verify and code the underlying immunocompromised condition. For B59, 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. 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, source-labeled coefficient references, 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