Q04.3
BillableOther reduction deformities of brain
Last updated: FY2026 ICD-10-CM (Oct 1, 2025 – Sep 30, 2026) | CMS-HCC V28 (100% phase-in, PY2026)
Is Q04.3 an HCC code?
Yes. Q04.3 maps to Spinal Cord Disorders/Injuries under the CMS-HCC V28 risk adjustment model (and Spinal Cord Disorders/Injuries 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 Q04.3
For Q04.3 to 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 Q04.3 during that encounter — not just copy-forwarded from a problem list.
What This Code Means
Q04.3 is the ICD-10-CM diagnosis code for other reduction deformities of brain. A birth defect involving various types of brain underdevelopment or reduction in brain tissue that do not fit into other specific categories. Q04.3 sits in the ICD-10-CM chapter for congenital malformations, deformations, chromosomal abnormalities, and genetic disorders (q00-qa0), within the section covering congenital malformations of the nervous system (q00-q07).
Under the CMS-HCC V28 risk adjustment model, Q04.3 maps to Spinal Cord Disorders/Injuries (HCC 182) with a community, non-dual, aged base RAF weight of 0.282. Under the older V24 model, Q04.3 mapped to the same category but with a base RAF weight of 0.464 — V28 recalibrated weights across the entire model. 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.
Use this code for brain reduction deformities not classified elsewhere. Because Q04.3 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 Q04.3 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
- •Use this code for brain reduction deformities not classified elsewhere
- •Document the specific type of reduction deformity when available
Clinical Significance
Other reduction deformities of the brain encompass various forms of underdevelopment or decreased brain tissue not classified elsewhere. These conditions require individualized assessment and management based on the specific areas affected and functional impact.
Documentation Requirements
- ✓Documentation of brain underdevelopment or reduction not fitting other categories
- ✓Neuroimaging findings showing decreased brain tissue or structures
- ✓Specific anatomical areas affected if identified
- ✓Neurological examination and functional assessment
- ✓Developmental evaluation and cognitive testing as appropriate
- ✓Associated complications or comorbidities
- ✓Exclusion of other specific brain malformation categories
- ✓Treatment and intervention planning
Excludes 1 — Do NOT code together
- congenital malformations of corpus callosum (Q04.0)