M35.9 ICD-10-CM Code: Systemic involvement of connective tissue, unspecified
HCC Buddy Code Card
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FY 2026 Apr update / Diseases of the musculoskeletal system and connective tissue (M00-M99) / Systemic connective tissue disorders (M30-M36)
M35.9
Billable / SpecificICD-10-CMOfficial ICD-10-CMCodebook guidanceSystemic involvement of connective tissue, unspecified
A general diagnosis indicating that connective tissue is affected throughout the body, but the specific type or extent of involvement has not been clearly identified.
Buddy Insight
Unspecified systemic connective tissue involvement indicates multi-organ autoimmune disease requiring further evaluation and specialist care, though the specific pattern hasn't been characterized.
CMS-HCC V28
00
RAF 0
CMS-HCC V24
MappedHCC 40
RAF 0.307
ACA/HHS
00
RAF 0
ESRD/PACE
MappedHCC 40
RAF 0.0
RXHCC
MappedHCC 84
RAF 0.0
Code Trumping
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Code Book Path
Inclusion Terms
Official- Autoimmune disease (systemic) NOS
- Collagen (vascular) disease NOS
Excludes 2
OfficialICD-10-CM does not list Excludes 2 notes for M35.9 in this effective period.
Related Child Codes
Includes
OfficialICD-10-CM does not list Includes notes for M35.9 in this effective period.
Excludes 1
Official- reactive perforating collagenosis (L87.1)
Code First
OfficialICD-10-CM does not list Code First sequencing instructions for M35.9 in this effective period.
Use Additional
OfficialICD-10-CM does not list Use Additional Code instructions for M35.9 in this effective period.
Code Also
OfficialICD-10-CM does not list Code Also instructions for M35.9 in this effective period.
Buddy Documentation Tip
MEAT Support
Audit Caution
Common Mistakes
Last updated: FY2026 ICD-10-CM Apr update, Apr 1, 2026 through Sep 30, 2026. CMS-HCC V28 is 100% phased in for payment year 2026.
Is M35.9 an HCC code?
Yes. M35.9 maps to Rheumatoid Arthritis and Inflammatory Connective Tissue Disease under the V24 model but is not retained in V28.
HCC Category Mapping
RAF weights shown are the community, non-dual, aged base weights from the CMS risk adjustment model file. Actual per-patient RAF contribution depends on member segment, interactions, and the model year used by the payer. V28 is the CMS-HCC model phased in over payment years 2024–2026; V24 remains in use during the transition and for historical data.
MEAT Criteria for M35.9
For M35.9to count as a valid HCC diagnosis in a given encounter, the provider's documentation must show MEAT: Monitor, Evaluate, Assess, or Treat. A diagnosis from a prior year does not carry forward automatically, it has to be re-documented and supported each calendar year.
- 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
Only one of M/E/A/T is required to support the code, but the documentation must be specific enough to show that the provider actually addressed M35.9 during that encounter, not just copy-forwarded from a problem list.
What This Code Means
M35.9 is the ICD-10-CM diagnosis code for systemic involvement of connective tissue, unspecified. A general diagnosis indicating that connective tissue is affected throughout the body, but the specific type or extent of involvement has not been clearly identified. M35.9 sits in the ICD-10-CM chapter for diseases of the musculoskeletal system and connective tissue (m00-m99), within the section covering systemic connective tissue disorders (m30-m36).
Under the older CMS-HCC V24 model, M35.9 maps to Rheumatoid Arthritis and Inflammatory Connective Tissue Disease (HCC 40) with a community, non-dual, aged base RAF weight of 0.307. V28 is the CMS-HCC risk adjustment model that reached 100% phase-in for payment year 2026, replacing V24 which was used during the PY2024–PY2025 transition.
This is a non-specific code; attempt to obtain more specific diagnosis information from the provider before coding. Because M35.9 maps to a payment HCC, the provider's documentation must satisfy MEAT criteria (Monitor, Evaluate, Assess, or Treat) for the encounter to count toward the patient's Medicare Advantage risk adjustment score. 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, RAF weights, and MEAT documentation criteria for M35.9 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
- •This is a non-specific code; attempt to obtain more specific diagnosis information from the provider before coding
- •Use only when the systemic connective tissue involvement cannot be classified to a more specific M35 code
Clinical Significance
Unspecified systemic connective tissue involvement indicates multi-organ autoimmune disease requiring further evaluation and specialist care, though the specific pattern hasn't been characterized. This diagnosis suggests the need for comprehensive rheumatologic assessment and monitoring.
Documentation Requirements
- ✓Documentation of systemic connective tissue disease features
- ✓Evidence of multi-organ involvement
- ✓Laboratory findings suggestive of autoimmune process
- ✓Clinical manifestations affecting multiple systems
- ✓Exclusion of other systemic diseases
- ✓Assessment of functional impact and disease severity
- ✓Plan for further diagnostic evaluation and specialist referral
Commonly Confused Codes
- •M35.89: Other specified systemic involvement of connective tissue (more specific)
- •M79.9: Soft tissue disorder, unspecified (localized rather than systemic)
- •R68.89: Other general symptoms and signs (lacks connective tissue component)
- •M25.9: Joint disorder, unspecified (joint-specific rather than systemic)
- •D89.9: Disorder involving the immune mechanism, unspecified (broader category)