2026 ICD-10-CM Diagnosis Code B59Pneumocystosis
ICD-10-CM Codes›A00–B99›B50-B64›B59
- Billable — Valid for Submission
- MCC — Major Complication or Comorbidity
- Risk Adjusts — HCC 6
- Not Chronic
B59 is a billable ICD-10-CM diagnosis code for pneumocystosis. It is valid on HIPAA claims for fiscal year 2026 (October 1, 2025 through September 30, 2026) and groups to MS-DRG 177 through 179, 791, 793, 974 through 976. As a secondary diagnosis, it counts as a major complication or comorbidity (MCC) and places an inpatient stay in the highest severity level of its MS-DRG family. It does not count, however, when the principal diagnosis is one of 105 closely related codes. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Fungal infections and Pneumonia (except that caused by tuberculosis).
For Medicare Advantage risk adjustment, B59 maps to CMS-HCC Category 6 (Opportunistic Infections) under the V28 model, adding a risk factor of about 0.381 for a community, non-dual, aged beneficiary in payment year 2026.
Code Identity
Code Classification
Medicare Risk Adjustment (HCC)Billing
B59 maps to a payment category in the CMS-HCC model used to risk-adjust Medicare Advantage payments. Weights are the published community factors for payment year 2026.
Source: CMS Payment Year 2026 risk adjustment mappings and model software. Weights are relative factors, not dollar amounts; a beneficiary's total RAF also includes demographics and interactions. Browse all CMS-HCC categories.
Approximate SynonymsGuidance
Alternate terms and clinical phrases that map to this code.
- Colonization of respiratory tract caused by Pneumocystis jirovecii
- Disseminated pneumocystosis
- Extrapulmonary pneumocystis infection
- Fungal choroiditis
- Infection by Pneumocystis jirovecii
- Infection caused by Pneumocystis co-occurrent with human immunodeficiency virus infection
- Infection of lung caused by Pneumocystis
- Inflammation of choroid caused by Pneumocystis jirovecii
- Lung cyst
- Pneumocystis jirovecii lung cyst
- Pneumocystis jirovecii present
- Pneumocystosis
- Pneumocystosis pneumonia
- Pneumocystosis with AIDS
- Pulmonary nodule caused by Pneumocystis
- Spontaneous pneumothorax
- Spontaneous pneumothorax due to infection caused by Pneumocystis jirovecii
- Spontaneous pneumothorax due to respiratory disease
Tabular List NotesGuidance
Coding notes and annotation back-references applicable to this code.
Inclusion Terms
- Pneumonia due to Pneumocystis carinii
- Pneumonia due to Pneumocystis jirovecii
These terms are the conditions for which that code is to be used. The terms may be synonyms of the code title, or, in the case of "other specified" codes, the terms are a list of the various conditions assigned to that code. The inclusion terms are not necessarily exhaustive. Additional terms found only in the Alphabetic Index may also be assigned to a code.
Index to Diseases and InjuriesGuidance
Clinical ClassificationClinical
AHRQ’s CCSR groups this code into broader clinical categories.
Patient EducationClinical
Pneumocystis Infections
Pneumocystis jirovecii is a fungus that is common throughout the world. Many people have been exposed to it as children. Some people have the fungus in their lungs. If you are healthy, it usually will not make you sick. But it can make you sick if you have a weakened immune system, for example if you:
The full article covers:
- What is Pneumocystis jirovecii?
- How does Pneumocystis jirovecii spread?
- What is pneumocystis pneumonia (PCP)?
- What are the symptoms of pneumocystis pneumonia (PCP)?
- How is pneumocystis pneumonia (PCP) diagnosed?
- What are the treatments for pneumocystis pneumonia (PCP)?
- Can pneumocystis pneumonia (PCP) be prevented?
Read the full article at MedlinePlus
Courtesy of MedlinePlus, a service of the U.S. National Library of Medicine.
Convert B59 to ICD-9-CMHistory
The closest ICD-9-CM equivalents under the General Equivalence Mappings.
Code HistoryHistory
Questions About B59Overview
What is the ICD-10 code for pneumocystosis?
The ICD-10-CM code for pneumocystosis is B59. It is billable on HIPAA-covered claims from October 1, 2025 through September 30, 2026.
Is B59 (Pneumocystosis) a billable code?
Yes. This is a billable ICD-10-CM code, specific enough to report pneumocystosis on HIPAA-covered claims from October 1, 2025 through September 30, 2026.
What MS-DRG does B59 group to?
When pneumocystosis is the principal diagnosis on an inpatient stay, it groups to MS-DRG 177, 178, 179, 791, 793, 974, 975, 976, with relative weights from 0.7550 to 4.1696 depending on complications. Higher weights mean higher Medicare reimbursement.
Is B59 a CC or MCC?
CMS lists B59 as an MCC (major complication or comorbidity) for FY 2026. Reported as a secondary diagnosis, it places the inpatient stay in the highest-weighted DRG of its severity family. It does not count when the principal diagnosis is one of the 105 closely related codes in its exclusion list.
What is the ICD-9 equivalent of B59?
Under the General Equivalence Mappings, pneumocystosis converts to ICD-9-CM 136.3 (pneumocystosis). The mapping is a direct match.
What HCC is B59?
B59 (pneumocystosis) maps to CMS-HCC Category 6 (Opportunistic Infections), commonly written as HCC 6, in the CMS-HCC V28 model used for Medicare Advantage risk adjustment in payment year 2026. It mapped to HCC 6 under the retired V24 model. It also maps in the PACE (CMS-HCC V22), ESRD (V21), and ESRD (V24) models. In the Part D prescription drug model it maps to RxHCC 5.
Does B59 risk-adjust for Medicare Advantage payment?
Yes. When documented and reported on a Medicare Advantage encounter, B59 adds a risk adjustment factor of about 0.381 to the beneficiary's RAF score for a community, non-dual, aged enrollee (published V28 weights range from 0.381 to 0.833 depending on the payment segment). HCC 6 sits at the top of its hierarchy, so no other condition category supersedes it. See the full factor table on the HCC 6 category page.
