P91.821
BillableNeonatal cerebral infarction, right side of brain
Last updated: FY2026 ICD-10-CM (Oct 1, 2025 – Sep 30, 2026) | CMS-HCC V28 (100% phase-in, PY2026)
Is P91.821 an HCC code?
Yes. P91.821 maps to Ischemic or Unspecified Stroke under the CMS-HCC V28 risk adjustment model (and Ischemic or Unspecified Stroke 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 P91.821
For P91.821 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 P91.821 during that encounter — not just copy-forwarded from a problem list.
What This Code Means
P91.821 is the ICD-10-CM diagnosis code for neonatal cerebral infarction, right side of brain. A newborn's stroke affecting the right side of the brain, caused by blocked blood flow to brain tissue. P91.821 sits in the ICD-10-CM chapter for certain conditions originating in the perinatal period (p00-p96), within the section covering other disorders originating in the perinatal period (p90-p96).
Under the CMS-HCC V28 risk adjustment model, P91.821 maps to Ischemic or Unspecified Stroke (HCC 249) with a community, non-dual, aged base RAF weight of 0.289. Under the older V24 model, P91.821 mapped to the same category but with a base RAF weight of 0.262 — 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.
Confirm documentation specifies the right hemisphere involvement; do not assume laterality without explicit documentation. Because P91.821 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 P91.821 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
- •Confirm documentation specifies the right hemisphere involvement; do not assume laterality without explicit documentation
- •Coordinate with imaging reports (MRI/CT) to verify the documented side of infarction
Clinical Significance
Neonatal cerebral infarction affecting the right brain represents acute stroke in newborns, causing tissue death and potential lifelong neurological deficits. This diagnosis indicates high risk for cerebral palsy affecting the left side of the body, developmental delays, and cognitive impairment.
Documentation Requirements
- ✓Clear documentation of cerebral infarction in newborn
- ✓Neuroimaging confirming infarct location on right side of brain
- ✓Clinical signs consistent with stroke (focal weakness, seizures)
- ✓Timing of infarct occurrence documented
- ✓Underlying risk factors identified (cardiac, infectious, genetic)
- ✓Extent and location of brain tissue involvement
- ✓Response to acute stroke management if applicable
- ✓Neurological examination findings and laterality