2026 ICD-10-CM Diagnosis Code D89.9Disorder involving the immune mechanism, unspecified
ICD-10-CM Codes›D50–D89›D80-D89›D89
- Billable — Valid for Submission
- Chronic Condition
D89.9 is a billable ICD-10-CM diagnosis code for disorder involving the immune mechanism, unspecified. It is valid on HIPAA claims for fiscal year 2026 (October 1, 2025 through September 30, 2026) and groups to MS-DRG 814 through 816. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Immunity disorders.
D89.9 no longer risk-adjusts for Medicare Advantage: it mapped to HCC 47 under the retired CMS-HCC V24 model through payment year 2025 but maps to no category in the live V28 model. It still risk-adjusts in the PACE (CMS-HCC V22) category 47, ESRD (V21) category 47, ESRD (V24) category 47, and RxHCC Part D (V08) category 99 for payment year 2026.
Code Identity
Code Classification
Medicare Risk Adjustment (HCC)Billing
D89.9 no longer risk-adjusts for Medicare Advantage: it maps to no payment category in the live CMS-HCC V28 model, although it still risk-adjusts in the other CMS models shown below.
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.
- Abnormal host defense
- Abnormal host response
- Acquired ataxia
- Acute nephritis due to another disorder
- Acute tubulointerstitial nephritis
- Acute tubulo-interstitial nephritis due to immunological disorder
- Antibody-mediated activation and inactivation
- Ataxia due to disorder of immune function
- Autoimmune AND/OR graft reaction
- Autoimmune reaction
- Autoimmune state
- Autoimmune vasculitis
- Autonomic neuropathy due to disorder of immune function
- Chorea due to immunological disorder
- Chronic disease of immune function
- Chronic disease of immune structure
- Cryopathy
- Disorder of immune function
- Disorder of immune function due to systemic lupus erythematosus
- Disorder of immune structure
- Drug-induced autoimmune reaction
- Epilepsy due to immune disorder
- Glomerular disorders in blood diseases and disorders involving the immune mechanism
- Granulocyte abnormality due to immune defect
- Hereditary disorder of immune system
- Hypertrophic pachymeningitis due to disorder of immune function
- Immune defect
- Immune system complication of procedure
- Immune-mediated neuropathy
- Immunosuppression-related infectious disease
- Induced autoimmune reaction
- Microcephaly, hypogammaglobulinemia, abnormal immunity syndrome
- Nonspecific immune reaction
- Pachymeningitis
- Panniculitis due to immunological disorder
- Postvaccinal autoimmune reaction
- Spondyloenchondrodysplasia
- Spondyloenchondrodysplasia with immune dysregulation
- Ulcer of esophagus due to disorder of immune system
Tabular List NotesGuidance
Coding notes and annotation back-references applicable to this code.
Inclusion Terms
- Immune disease NOS
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
Alphabetical index entries that point to this code.
Disease, diseased See Also: Syndrome;
immune D89.9
Disorder (of) See Also: Disease;
Clinical ClassificationClinical
AHRQ’s CCSR groups this code into broader clinical categories.
Patient EducationClinical
Immune System and Disorders
Your immune system is a complex network of cells, tissues, and organs. Together they help the body fight infections and other diseases.
The full article covers:
- What is the immune system?
- What are the parts of the immune system?
- How does the immune system work?
- What are the types of immunity?
- What can go wrong with the immune system?
Read the full article at MedlinePlus
Courtesy of MedlinePlus, a service of the U.S. National Library of Medicine.
Convert D89.9 to ICD-9-CMHistory
The closest ICD-9-CM equivalents under the General Equivalence Mappings.
Code HistoryHistory
Questions About D89.9Overview
What is the ICD-10 code for disorder involving the immune mechanism, unspecified?
The ICD-10-CM code for disorder involving the immune mechanism, unspecified is D89.9 (sometimes written as D899). It is billable on HIPAA-covered claims from October 1, 2025 through September 30, 2026.
Is D89.9 a billable code?
Yes. This is a billable ICD-10-CM code, specific enough to report disorder involving the immune mechanism, unspecified on HIPAA-covered claims from October 1, 2025 through September 30, 2026.
What MS-DRG does D89.9 group to?
When disorder involving the immune mechanism, unspecified is the principal diagnosis on an inpatient stay, it groups to MS-DRG 814, 815, 816, with relative weights from 0.6320 to 2.1267 depending on complications. Higher weights mean higher Medicare reimbursement.
What is the ICD-9 equivalent of D89.9?
Under the General Equivalence Mappings, disorder involving the immune mechanism, unspecified converts to ICD-9-CM 279.9 (immune mechanism dis NOS). The mapping is a direct match.
Does D89.9 risk-adjust for Medicare Advantage payment?
Not for Medicare Advantage. D89.9 mapped to HCC 47 in the retired CMS-HCC V24 model, which last determined payment in 2025, but it maps to no category in the live V28 model; see all codes that no longer risk-adjust. It still risk-adjusts in the PACE (CMS-HCC V22) category 47 (Disorders of Immunity), ESRD (V21) category 47 (Disorders of Immunity), ESRD (V24) category 47 (Disorders of Immunity), and RxHCC Part D (V08) category 99 (Immune Disorders).
