2027 ICD-10-CM Diagnosis Code B26.85Mumps arthritis
ICD-10-CM Codes›A00–B99›B25-B34›B26
- Billable — Valid for Submission
- CC — Complication or Comorbidity
- Risk Adjusts — HCC 92
- Not Chronic
B26.85 is a billable ICD-10-CM diagnosis code for mumps arthritis. It is valid on HIPAA claims for fiscal year 2027 (October 1, 2026 through September 30, 2027) and groups to MS-DRG 791, 793, 865 through 866. As a secondary diagnosis, it counts as a complication or comorbidity (CC) and moves an inpatient stay to a higher severity level within its MS-DRG family. It does not count, however, when the principal diagnosis is one of 22 closely related codes. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Infective arthritis and Viral infection.
For Medicare Advantage risk adjustment, B26.85 maps to CMS-HCC Category 92 (Bone/Joint/Muscle/Severe Soft Tissue Infections/Necrosis) under the V28 model, adding a risk factor of about 0.479 for a community, non-dual, aged beneficiary in payment year 2027.
Code Identity
Code Classification
Medicare Risk Adjustment (HCC)Billing
B26.85 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.
- Mumps arthritis
Instructional NotesGuidance
Instructions from the official ICD-10-CM Tabular List that apply to B26.85: its own notes plus those printed at B26 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.
- epidemic parotitis
- infectious parotitis
- diseases generally recognized as communicable or transmissible
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 B26.85, its category, or a range that includes it.
Applicable To 1
These notes mention B26.85.
- O98.5 Other viral diseases complicating pregnancy, childbirth and the puerperium
Excludes1 4
These codes carry an Excludes1 note naming B26.85: they are not reported together with it, unless the two conditions are unrelated.
- M01 Direct infections of joint in infectious and parasitic diseases classified elsewheremumps arthritis (B26.85)
- M02 Postinfective and reactive arthropathiesmumps arthritis (B26.85)
- K11.2 Sialoadenitisepidemic parotitis (B26.-) names B26.-, which includes this code
- K11.2 Sialoadenitismumps (B26.-) names B26.-, which includes this 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.
Clinical InformationClinical
Mumps
an acute infectious disease caused by rubulavirus, spread by direct contact, airborne droplet nuclei, fomites contaminated by infectious saliva, and perhaps urine, and usually seen in children under the age of 15, although adults may also be affected. (from dorland, 28th ed)
Patient EducationClinical
Mumps
Mumps is an illness caused by the mumps virus. It starts with:
Read the full article at MedlinePlus
Courtesy of MedlinePlus, a service of the U.S. National Library of Medicine.
Convert B26.85 to ICD-9-CMHistory
The closest ICD-9-CM equivalents under the General Equivalence Mappings.
Code HistoryHistory
Questions About B26.85Overview
What is the ICD-10 code for mumps arthritis?
The ICD-10-CM code for mumps arthritis is B26.85 (sometimes written as B2685). It is billable on HIPAA-covered claims from October 1, 2026 through September 30, 2027.
Is B26.85 (Mumps with other complications) a billable code?
Yes. This is a billable ICD-10-CM code, specific enough to report mumps arthritis on HIPAA-covered claims from October 1, 2026 through September 30, 2027.
What MS-DRG does B26.85 group to?
When mumps arthritis is the principal diagnosis on an inpatient stay, it groups to MS-DRG 793, 791, 866, 865, with relative weights from 0.8691 to 4.2192 depending on complications. Higher weights mean higher Medicare reimbursement.
Is B26.85 a CC or MCC?
CMS lists B26.85 as a CC (complication or comorbidity) for FY 2027. Reported as a secondary diagnosis, it moves the inpatient stay to a higher-weighted DRG within its severity family. It does not count when the principal diagnosis is one of the 22 closely related codes in its exclusion list.
What is the ICD-9 equivalent of B26.85?
Under the General Equivalence Mappings, mumps arthritis converts to ICD-9-CM 072.79 (mumps complication NEC). The mapping is approximate, so confirm the match fits the documentation.
What HCC is B26.85?
B26.85 (mumps arthritis) maps to CMS-HCC Category 92 (Bone/Joint/Muscle/Severe Soft Tissue Infections/Necrosis), commonly written as HCC 92, in the CMS-HCC V28 model used for Medicare Advantage risk adjustment in payment year 2027. It mapped to HCC 39 under the retired V24 model. It also maps in the PACE (CMS-HCC V22), ESRD (V21), and ESRD (V24) models. It does not map to any RxHCC in the Part D prescription drug model.
Does B26.85 risk-adjust for Medicare Advantage payment?
Yes. When documented and reported on a Medicare Advantage encounter, B26.85 adds a risk adjustment factor of about 0.479 to the beneficiary's RAF score for a community, non-dual, aged enrollee (published V28 weights range from 0.471 to 0.632 depending on the payment segment). HCC 92 sits at the top of its hierarchy, so no other condition category supersedes it. See the full factor table on the HCC 92 category page.
