2026 ICD-10-CM Diagnosis Code D89.49Other mast cell activation disorder
ICD-10-CM Codes›D50–D89›D80-D89›D89
- Billable — Valid for Submission
- Chronic Condition
D89.49 is a billable ICD-10-CM diagnosis code for other mast cell activation disorder. 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.
D89.49 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
D89.49 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.
Tabular List NotesGuidance
Coding notes and annotation back-references applicable to this code.
Inclusion Terms
- Other mast cell activation syndrome
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.
Clinical ClassificationClinical
AHRQ’s CCSR groups this code into broader clinical categories.
Convert D89.49 to ICD-9-CMHistory
The closest ICD-9-CM equivalents under the General Equivalence Mappings.
Code History & ChangesHistory
Replacement D89.49 replaces the following previously assigned code(s):
- D89.89 - Oth disrd involving the immune mechanism, NEC
Questions About D89.49Overview
What is the ICD-10 code for other mast cell activation disorder?
The ICD-10-CM code for other mast cell activation disorder is D89.49 (sometimes written as D8949). It is billable on HIPAA-covered claims from October 1, 2025 through September 30, 2026.
Is D89.49 (Mast cell activation syndrome and related disorders) a billable code?
Yes. This is a billable ICD-10-CM code, specific enough to report other mast cell activation disorder on HIPAA-covered claims from October 1, 2025 through September 30, 2026.
What MS-DRG does D89.49 group to?
When other mast cell activation disorder 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 D89.49?
Under the General Equivalence Mappings, other mast cell activation disorder converts to ICD-9-CM 279.8 (immune mechanism dis NEC). The mapping is approximate, so confirm the match fits the documentation.
Does D89.49 risk-adjust for Medicare Advantage payment?
Not for Medicare Advantage. D89.49 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).
