G40.843 ICD-10-CM Code: KCNQ2-related epilepsy, intractable, with status epilepticus
HCC Buddy Code Card
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FY 2026 Apr update / Diseases of the nervous system (G00-G99) / Episodic and paroxysmal disorders (G40-G47)
G40.843
Billable / SpecificICD-10-CMOfficial ICD-10-CMCodebook guidanceKCNQ2-related epilepsy, intractable, with status epilepticus
Epilepsy caused by a KCNQ2 gene mutation that does not respond well to medication, currently experiencing a prolonged seizure state.
Buddy Insight
KCNQ2-related epilepsy, intractable, with status epilepticus indicates the severe KCNQ2 encephalopathy phenotype with drug-resistant seizures in active status epilepticus.
CMS-HCC V28
MappedHCC 201
RAF 0.262
CMS-HCC V24
MappedHCC 79
RAF 0.244
ACA/HHS
00
RAF 0
ESRD/PACE
MappedHCC 79
RAF 0.0
RXHCC
MappedHCC 163
RAF 0.0
Code Trumping
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Code Book Path
Inclusion Terms
OfficialICD-10-CM does not list inclusion terms for G40.843 in this effective period.
Excludes 2
OfficialICD-10-CM does not list Excludes 2 notes for G40.843 in this effective period.
Related Child Codes
Includes
OfficialICD-10-CM does not list Includes notes for G40.843 in this effective period.
Excludes 1
OfficialICD-10-CM does not list Excludes 1 notes for G40.843 in this effective period.
Code First
OfficialICD-10-CM does not list Code First sequencing instructions for G40.843 in this effective period.
Use Additional
OfficialICD-10-CM does not list Use Additional Code instructions for G40.843 in this effective period.
Code Also
OfficialICD-10-CM does not list Code Also instructions for G40.843 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 G40.843 an HCC code?
Yes. G40.843 maps to Seizure Disorders and Convulsions under the CMS-HCC V28 risk adjustment model (and Seizure Disorders and Convulsions 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 G40.843
For G40.843to 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 G40.843 during that encounter, not just copy-forwarded from a problem list.
What This Code Means
G40.843 is the ICD-10-CM diagnosis code for kcnq2-related epilepsy, intractable, with status epilepticus. Epilepsy caused by a KCNQ2 gene mutation that does not respond well to medication, currently experiencing a prolonged seizure state. G40.843 sits in the ICD-10-CM chapter for diseases of the nervous system (g00-g99), within the section covering episodic and paroxysmal disorders (g40-g47).
Under the CMS-HCC V28 risk adjustment model, G40.843 maps to Seizure Disorders and Convulsions (HCC 201) with a community, non-dual, aged base RAF weight of 0.262. Under the older V24 model, G40.843 mapped to the same category but with a base RAF weight of 0.244, 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 KCNQ2 mutation through genetic testing documentation. Because G40.843 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 G40.843 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
- •Confirm KCNQ2 mutation through genetic testing documentation
- •Document both intractable status (failed medication trials) and active status epilepticus
Clinical Significance
KCNQ2-related epilepsy, intractable, with status epilepticus indicates the severe KCNQ2 encephalopathy phenotype with drug-resistant seizures in active status epilepticus. This represents a neurological emergency in a patient with a known genetic channelopathy. These patients typically have the more severe KCNQ2 variants associated with encephalopathy, intellectual disability, and poor seizure control.
Documentation Requirements
- ✓Genetic confirmation of KCNQ2 mutation
- ✓Documentation of intractability with failed medication trials
- ✓Active status epilepticus during the encounter
- ✓Emergency interventions provided
- ✓Complete medication history including response to sodium channel blockers
- ✓Neurodevelopmental status
Commonly Confused Codes
- •G40.841 — KCNQ2 epilepsy with status epilepticus but NOT intractable
- •G40.844 — KCNQ2 epilepsy, intractable, WITHOUT status epilepticus
- •G40.833 — Dravet syndrome, intractable, with status epilepticus; different genetic epilepsy (SCN1A)
- •G40.803 — Other epilepsy, intractable, with status epilepticus; less specific
- •G40.823 — Epileptic spasms, intractable, with status epilepticus