B26.85 ICD-10-CM Code: Mumps arthritis
B26.85 maps to CMS-HCC V28 92. A source-labeled RAF reference is available. Confirm the documented diagnosis and applicable coding requirements. MEAT criteria · RAF Calculator · HCC coding software
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FY 2026 Apr update / Certain infectious and parasitic diseases (A00-B99) / Other viral diseases (B25-B34)
B26.85
Billable / SpecificICD-10-CMOfficial ICD-10-CMCodebook guidanceMumps arthritis
Inflammation of the joints (arthritis) caused by the mumps virus, occurring as a complication of mumps infection.
Buddy Insight
Mumps arthritis is an uncommon but recognized complication of mumps virus infection, occurring in approximately 0.
CMS-HCC V28
MappedHCC 92
Coefficient HCC 92: 0.479 (Community Non-Dual Aged (CNA))
CMS-HCC V24
HistoricalHistorical
Not used for CY2026 payment
ACA/HHS
MappedHCC 055
Code-level coefficient reference
ESRD/PACE
MappedHCC 39
Code-level coefficient reference
RXHCC
N/A—
Not mapped
Code Book Path
Inclusion Terms
OfficialNo inclusion terms are included in this display for B26.85. Check the code and parent instructions in the Code Book.
Excludes 2
Official- carrier or suspected carrier of infectious disease (Z22.-)Inherited from A00-B99
- infectious and parasitic diseases complicating pregnancy, childbirth and the puerperium (O98.-)Inherited from A00-B99
- infectious and parasitic diseases specific to the perinatal period (P35-P39)Inherited from A00-B99
- influenza and other acute respiratory infections (J00-J22)Inherited from A00-B99
Related Codes
Includes
Official- diseases generally recognized as communicable or transmissibleInherited from A00-B99, B26
- epidemic parotitisInherited from A00-B99, B26
- infectious parotitisInherited from A00-B99, B26
Excludes 1
Official- certain localized infections - see body system-related chaptersInherited from A00-B99
Code First
OfficialNo Code First sequencing instructions are included in this display for B26.85. Check the code and parent instructions in the Code Book.
Use Additional
Official- code to identify resistance to antimicrobial drugs (Z16.-)Inherited from A00-B99
Code Also
OfficialNo Code Also instructions are included in this display for B26.85. Check the code and parent instructions in the Code Book.
Buddy Documentation Tip
MEAT Support
Audit Caution
Common Mistakes
Current with CMS: FY2026 ICD-10-CM Apr 1 update (effective Apr 1 – Sep 30, 2026) · CMS-HCC V28, 100% phased in for payment year 2026. FY2027 code set already staged for October 1, 2026. How HCC Buddy stays current →
Is B26.85 an HCC code?
Yes. B26.85 (Mumps arthritis) maps to HCC 92, Bone/Joint/Muscle/Severe Soft Tissue Infections/Necrosis under the CMS-HCC V28 risk adjustment model, with a source-labeled community non-dual aged reference coefficient of 0.479. Source-labeled code-level coefficients are references, not member totals. Actual contribution depends on complete member context, hierarchy and cleanup rules, interactions, and model year. HCC Buddy's RAF Calculator supports CMS-HCC V28 PY2026 and shows no score unless every required source and calculation check passes. It is billable for payment year 2026.
Coder answer: B26.85 is billable and maps to V28 HCC 92, Bone/Joint/Muscle/Severe Soft Tissue Infections/Necrosis. Open it in the Code Book for the tabular path, RAF, and MEAT checklist.
- Code
- B26.85
- Description
- Mumps arthritis
- HCC (V28)
- HCC 92 — Bone/Joint/Muscle/Severe Soft Tissue Infections/Necrosis
- RAF reference coefficient
- 0.479
- Billable
- Yes
- Payment year
- 2026
HCC Category Mapping
These are source-labeled model coefficients, not member totals. A category may still be removed by hierarchy or model cleanup rules. Weights are not directly comparable across models: CMS-HCC V28 and V24 use Community, Non-Dual, Aged; ESRD uses the dialysis continuing-enrollee model; RxHCC is the Part D continuing-enrollee, non-low-income, aged weight (a larger scale than CMS-HCC). ACA/HHS has no single weight — it varies by metal level. Actual per-patient RAF contribution depends on member context, hierarchy and cleanup rules, interactions, and the model year used by the payer. V28 is the CMS-HCC model phased in over payment years 2024–2026; V24 remains available for historical review.
Work B26.85 in the Code Book — tabular path, V28 RAF reference, and MEAT checklist →
MEAT review for B26.85
For B26.85, confirm that the documentation supports the diagnosis and meets the applicable coding, encounter, program and payer requirements. MEAT (Monitor, Evaluate, Assess, or Treat) is a review mnemonic, not a universal CMS coding rule.
- MMonitor: signs, symptoms, disease progression, or lab trending documented in the note
- EEvaluate: test results, medication response, or physical findings reviewed by the provider
- AAssess: explicit mention in the assessment or plan with acknowledgment of status
- TTreat: medication, referral, procedure, therapy, or counseling tied to the diagnosis
Coder workflow notes
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What This Code Means
B26.85 is the ICD-10-CM diagnosis code for mumps arthritis. Inflammation of the joints (arthritis) caused by the mumps virus, occurring as a complication of mumps infection. B26.85 sits in the ICD-10-CM chapter for certain infectious and parasitic diseases (a00-b99), within the section covering other viral diseases (b25-b34).
Under the CMS-HCC V28 risk adjustment model, B26.85 maps to Bone/Joint/Muscle/Severe Soft Tissue Infections/Necrosis (HCC 92) with a source-labeled community, non-dual, aged reference coefficient of 0.479. For CY2026 non-PACE Medicare Advantage, CMS uses 100% of the 2024 CMS-HCC model (V28). PACE uses a separate model blend. Source-labeled code-level coefficients are references, not member totals. Actual contribution depends on complete member context, hierarchy and cleanup rules, interactions, and model year. HCC Buddy's RAF Calculator supports CMS-HCC V28 PY2026 and shows no score unless every required source and calculation check passes.
Document which joints are affected and whether symptoms are symmetric or asymmetric. For B26.85, confirm that the documentation supports the diagnosis and meets the applicable coding, encounter, program and payer requirements. MEAT (Monitor, Evaluate, Assess, or Treat) is a review mnemonic, not a universal CMS coding rule. When documentation is ambiguous, coders should issue a provider query rather than assume the highest-specificity variant.
HCC Buddy maintains structured V28 and V24 mapping, source-labeled coefficient references, and MEAT documentation criteria for B26.85 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
- •Document which joints are affected and whether symptoms are symmetric or asymmetric
- •Mumps arthritis is typically self-limited; specify if monoarticular or polyarticular involvement
Clinical Significance
Mumps arthritis is an uncommon but recognized complication of mumps virus infection, occurring in approximately 0.4% of mumps cases. It typically presents as a migratory polyarthritis affecting large joints and is usually self-limited, resolving within weeks. In the era of widespread MMR vaccination, this condition is rare but may be seen during outbreaks.
Documentation Requirements
- ✓Confirmed mumps infection (positive mumps IgM or viral PCR)
- ✓Joint involvement documented: specific joints affected, symmetry, duration
- ✓Timeline of arthritis relative to parotitis or other mumps symptoms
- ✓MMR vaccination history
- ✓Clinical course documentation: onset, peak, resolution