2026 ICD-10-CM Diagnosis Code B59Pneumocystosis

ICD-10-CM Codes›A00–B99›B50-B64›B59

ICD-10-CM B59
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

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, 974 through 976. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Fungal infections and Pneumonia (except that caused by tuberculosis).

Code Identity

ICD-10-CM Code
B59
Billable Status
Yes — Valid for Submission
Code Describes
Pneumocystosis
Chapter
B50-B64
Protozoal diseases

Code Classification

ChapterA00–B99Certain infectious and parasitic diseases
SectionB50-B64Protozoal diseases
CategoryB59Pneumocystosis
This CodeB59Pneumocystosis

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

Index to Diseases and InjuriesGuidance

Alphabetical index entries that point to this code.

External Cause of Injuries IndexGuidance

References for this code in the External Cause of Injuries Index.

    • Disease, diseased
      • protozoal
        • pneumocystosis
    • Infection, infected, infective(opportunistic)
      • Pneumocystis carinii (pneumonia)
    • Infection, infected, infective(opportunistic)
      • Pneumocystis jirovecii (pneumonia)
    • Pneumocystis carinii pneumonia
    • Pneumocystis jirovecii(pneumonia)
    • Pneumocystosis(with pneumonia)
    • Pneumonia(acute) (double) (migratory) (purulent) (septic) (unresolved)
      • in (due to)
        • pneumocystosis (Pneumocystis carinii) (Pneumocystis jirovecii)
    • Pneumonia(acute) (double) (migratory) (purulent) (septic) (unresolved)
      • interstitial
        • plasma cell
    • Pneumonia(acute) (double) (migratory) (purulent) (septic) (unresolved)
      • plasma cell (of infants)
    • Pneumonia(acute) (double) (migratory) (purulent) (septic) (unresolved)
      • Pneumocystis (carinii) (jirovecii)

Clinical ClassificationClinical

AHRQ’s CCSR groups this code into broader clinical categories.

CCSR INF004
Fungal infections
Default principal diagnosis: inpatient No · outpatient No
CCSR RSP002
Pneumonia (except that caused by tuberculosis)
Default principal diagnosis: inpatient Yes · outpatient Yes

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.

ICD-9-CM
136.3 Pneumocystosis
Exact Match The mapping is direct, with no qualifiers.

Code HistoryHistory

FY 2016AddedAdded to the ICD-10-CM code setEffective October 1, 2015, the first year of ICD-10-CM.
FY 2017–2025No changes
FY 2026CurrentCurrent code set, no changesEffective October 1, 2025 through September 30, 2026.

Questions About B59Overview

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, 974, 975, 976, with relative weights from 0.7550 to 2.8860 depending on complications. Higher weights mean higher Medicare reimbursement.

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.

Footnotes

[1] Not chronic - A diagnosis code that does not fit the criteria for chronic condition (duration, ongoing medical treatment, and limitations) is considered not chronic. Some codes designated as not chronic are acute conditions. Other diagnosis codes that indicate a possible chronic condition, but for which the duration of the illness is not specified in the code description (i.e., we do not know the condition has lasted 12 months or longer) also are considered not chronic.