M04.1
BillablePeriodic fever syndromes
Last updated: FY2026 ICD-10-CM (Oct 1, 2025 – Sep 30, 2026) | CMS-HCC V28 (100% phase-in, PY2026)
Is M04.1 an HCC code?
Yes. M04.1 maps to Reactive and Specified Arthropathies under the CMS-HCC V28 risk adjustment model (and Rheumatoid Arthritis and Inflammatory Connective Tissue Disease under V24).
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 M04.1
For M04.1to 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 M04.1 during that encounter — not just copy-forwarded from a problem list.
What This Code Means
M04.1 is the ICD-10-CM diagnosis code for periodic fever syndromes. A group of rare genetic conditions characterized by recurring episodes of fever and inflammation throughout the body. M04.1 sits in the ICD-10-CM chapter for diseases of the musculoskeletal system and connective tissue (m00-m99), within the section covering autoinflammatory syndromes (m04).
Under the CMS-HCC V28 risk adjustment model, M04.1 maps to Reactive and Specified Arthropathies (HCC 94) with a community, non-dual, aged base RAF weight of 0.000. Under the older CMS-HCC V24 model, M04.1 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.
Periodic fever syndromes are autoinflammatory disorders; ensure documentation distinguishes these from autoimmune conditions. Because M04.1 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 M04.1 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
- •Periodic fever syndromes are autoinflammatory disorders; ensure documentation distinguishes these from autoimmune conditions
- •Specify the type of periodic fever syndrome if documented (such as PFAPA, FMF, or other variants) for more precise coding
Clinical Significance
This represents periodic fever syndromes, rare autoinflammatory conditions characterized by recurrent episodes of fever and systemic inflammation. These conditions require specialized management and monitoring due to their chronic nature and potential for serious complications including organ damage and amyloidosis.
Documentation Requirements
- ✓Documentation of recurrent fever episodes with characteristic patterns
- ✓Evidence of systemic inflammatory symptoms during fever episodes
- ✓Exclusion of infectious causes for recurrent fevers
- ✓Clinical assessment supporting autoinflammatory syndrome diagnosis
- ✓Documentation of fever periodicity and episode characteristics
- ✓Laboratory evidence of inflammation during acute episodes
- ✓Family history assessment for hereditary periodic fever syndromes
- ✓Response to specific treatments (colchicine, biologics) if applicable
Commonly Confused Codes
- •R50.9 — Fever, unspecified (symptom vs specific syndrome diagnosis)
- •M04.2 — Cryopyrin-associated periodic syndromes (specific vs general periodic fever)
- •D89.1 — Cryoglobulinemia (different autoinflammatory mechanism)
- •M35.9 — Systemic involvement of connective tissue, unspecified (autoimmune vs autoinflammatory)
- •A49.9 — Bacterial infection, unspecified (infectious vs autoinflammatory fever)