2027 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 2027 (October 1, 2026 through September 30, 2027) 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 2027.
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 2027.
Source: CMS Payment Year 2027 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 infection caused by Pneumocystis jirovecii
- Extrapulmonary pneumocystis jirovecii infection
- Fungal choroiditis
- Infection by Pneumocystis jirovecii
- Infection caused by Pneumocystis jirovecii with acquired immunodeficiency syndrome
- Infection caused by Pneumocystis jirovecii with infection caused by human immunodeficiency virus
- Infection of lung caused by Pneumocystis jirovecii
- Inflammation of choroid caused by Pneumocystis jirovecii
- Nodule of lung caused by Pneumocystis jirovecii
- Pneumocystis jirovecii lung cyst
- Pneumocystis jirovecii present
- Pneumocystosis jirovecii pneumonia
- Spontaneous pneumothorax
- Spontaneous pneumothorax due to infection caused by Pneumocystis jirovecii
- Spontaneous pneumothorax due to respiratory disease
Instructional NotesGuidance
Instructions from the official ICD-10-CM Tabular List that apply to B59: its own notes plus those printed at block B50-B64 and Chapter 1. A note printed at a category, block or chapter applies to every code under it.
Includes
Further defines, or gives examples of, the content of the category.
- diseases generally recognized as communicable or transmissible
Applicable To
Conditions this code is used for: synonyms of the title or, for "other specified" codes, the conditions assigned to it. The list is not exhaustive.
- Pneumonia due to Pneumocystis carinii
- Pneumonia due to Pneumocystis jirovecii
Excludes1
Not coded here: the excluded code is never reported together with this one, unless the two conditions are unrelated.
Excludes2
Not included here: the excluded condition is not part of this code, but a patient may have both, so both codes may be reported.
- carrier or suspected carrier of infectious disease (Z22.-)
- certain localized infections - see body system-related chapters
- infectious and parasitic diseases complicating pregnancy, childbirth and the puerperium (O98.-)
- infectious and parasitic diseases specific to the perinatal period (P35-P39)
- influenza and other acute respiratory infections (J00-J22)
Use Additional Code
Add a second code, after this one, to fully describe the condition.
- code to identify resistance to antimicrobial drugs (Z16.-)
Source: CMS ICD-10-CM Tabular List. How to read instructional notes.
Referenced in Other NotesGuidance
Instructional notes printed at other codes that name B59, its category, or a range that includes it.
Applicable To 1
These notes mention B59.
- O98.6 Protozoal diseases complicating pregnancy, childbirth and the puerperium
Excludes1 6
These codes carry an Excludes1 note naming B59: they are not reported together with it, unless the two conditions are unrelated.
- J16 Pneumonia due to other infectious organisms, not elsewhere classifiedpneumocystosis (B59)
- J17 Pneumonia in diseases classified elsewherepneumocystosis (B59)
- J17 Pneumonia in diseases classified elsewherepneumonia due to Pneumocystis carinii (B59)
- J17 Pneumonia in diseases classified elsewherepneumonia due to Pneumocystis jirovecii (B59)
- J84.11 Idiopathic interstitial pneumoniapneumocystis pneumonia (B59)
- J84.114 Acute interstitial pneumonitispneumocystis pneumonia (B59)
Code First 1
These codes say to code first a condition named in the note, and B59 is one of the conditions named.
- J93.12 Secondary spontaneous pneumothoraxpneumonia due to Pneumocystis carinii (B59)
Index to Diseases and InjuriesGuidance
Clinical ClassificationClinical
AHRQ’s CCSR groups this code into broader clinical categories.
Clinical InformationClinical
Pneumonia, Pneumocystis
a pulmonary disease in humans occurring in immunodeficient or malnourished patients or infants, characterized by dyspnea, tachypnea, and hypoxemia. pneumocystis pneumonia is a frequently seen opportunistic infection in aids. it is caused by the fungus pneumocystis jirovecii. the disease is also found in other mammals where it is caused by related species of pneumocystis.
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, 2026 through September 30, 2027.
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, 2026 through September 30, 2027.
What MS-DRG does B59 group to?
When pneumocystosis is the principal diagnosis on an inpatient stay, it groups to MS-DRG 793, 791, 974, 976, 975, 179, 178, 177, with relative weights from 0.7344 to 4.2192 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 2027. 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.
Can B59 be reported with a code from A06?
Not as a rule. The Excludes1 note at block B50-B64, which applies to B59, lists "amebiasis (A06.-)". An Excludes1 note means the excluded code is never reported together with this one; the only exception is when the two conditions are unrelated to each other (Official Guidelines, Section I.A.12.a).
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 2027. 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.
