Question 1

What is ICD-10 code G04.00?

Accepted Answer

G04.00 is the ICD-10-CM diagnosis code for acute disseminated encephalitis and encephalomyelitis, unspecified. Sudden inflammation of the brain and spinal cord affecting multiple areas, occurring without a known specific trigger. G04.00 sits in the ICD-10-CM chapter for diseases of the nervous system (g00-g99), within the section covering inflammatory diseases of the central nervous system (g00-g09).

G04.00 has no mapping under the CMS-HCC V28 or V24 community payment models. G04.00 also appears in the HHS-HCC commercial risk model (HCC 003 (HHS-HCC 003 adult, RAF varies by metal level)), which is a commercial market model rather than a Medicare Advantage payment mapping. Do not assign V28 risk adjustment value from this page; verify the applicable model and payment year before using this code for risk adjustment.

Distinguish between postinfectious ADEM (G04.01) and other causes of acute disseminated encephalitis.

Question 2

Is G04.00 an HCC code?

Accepted Answer

G04.00 has no payable CMS-HCC V28 mapping in the final FY2026 CMS file.

Question 3

Is G04.00 billable?

Accepted Answer

Yes. G04.00 is a billable ICD-10-CM code that can be reported on professional and institutional claims as a primary or secondary diagnosis when the provider documentation supports the specific condition described. Billable codes in ICD-10-CM are coded to the highest level of specificity available for the documented diagnosis. G04.00 is current for fiscal year 2026 and remains in the active CMS ICD-10-CM code set published by the National Center for Health Statistics.

Question 4

Which HCC does G04.00 map to under V28?

Accepted Answer

G04.00 has no payable CMS-HCC V28 mapping in the final FY2026 CMS file.

Question 5

What RAF reference is published for G04.00?

Accepted Answer

G04.00 has no V28 reference coefficient because the final FY2026 source verifies no payable V28 mapping.

Question 6

What is the V28 vs V24 difference for G04.00?

Accepted Answer

G04.00 has verified no payable V28 mapping in the final FY2026 source. Select a historical effective period before making any V24 comparison.

Question 7

What documentation supports G04.00?

Accepted Answer

Distinguish between postinfectious ADEM (G04.01) and other causes of acute disseminated encephalitis Document the extent of involvement (brain, spinal cord, or both) in clinical notes G04.00 is not a CMS-HCC V28 payment code in the verified current source, so MEAT is not the payment hook. Documentation still has to support the diagnosis if you report it.

Question 8

Can G04.00 be a primary diagnosis?

Accepted Answer

Yes. G04.00 carries no code-first instruction in the FY2026 tabular, so it can be the first-listed diagnosis when it is the condition chiefly responsible for the encounter and the note supports it, and it can also be reported as a secondary diagnosis. For risk adjustment the order does not matter; the V28 category is the same either way.

Question 9

Which codes cannot be reported with G04.00?

Accepted Answer

The Excludes1 note that applies to G04.00 lists encephalopathy NOS (G93.40); acute necrotizing hemorrhagic encephalopathy (G04.3-); other noninfectious acute disseminated encephalomyelitis (noninfectious ADEM) (G04.81). An Excludes1 condition is not reported together with G04.00; report one or the other, unless the two conditions are unrelated, which the ICD-10-CM Official Guidelines (Section I.A.12.a) allow. The Excludes2 note lists certain conditions originating in the perinatal period (P04-P96); certain infectious and parasitic diseases (A00-B99); complications of pregnancy, childbirth and the puerperium (O00-O9A); congenital malformations, deformations, and chromosomal abnormalities (Q00-Q99); and 11 more (see the notes on this page); those are separate conditions that may be reported together with G04.00 when both are documented.

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G04.00

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G04.00 ICD-10-CM Code: Acute disseminated encephalitis and encephalomyelitis, unspecified

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G04.00

Is G04.00 an HCC code?

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