Question 1

What is ICD-10 code A83.5?

Accepted Answer

A83.5 is the ICD-10-CM diagnosis code for California encephalitis. California encephalitis is a viral infection that causes inflammation of the brain, transmitted through mosquito bites. It can cause fever, headache, confusion, and in severe cases, neurological complications. A83.5 is a billable code, meaning it can be reported on a claim as a primary or secondary diagnosis when supported by documentation. A83.5 is part of the FY2026 ICD-10-CM code set published by the CMS National Center for Health Statistics and used on Medicare, Medicaid, and commercial claims in the United States.

Question 2

Is A83.5 an HCC code?

Accepted Answer

No. A83.5 is a billable ICD-10-CM code but does not map to any payment HCC category under the CMS-HCC V28, V24, ESRD, or RxHCC risk adjustment models. It can still be reported on Medicare Advantage encounter data submissions, but it does not contribute to the beneficiary's Risk Adjustment Factor (RAF) score and therefore does not affect the risk-adjusted capitation payment to the plan. V28 reached 100% phase-in for payment year 2026.

Question 3

Is A83.5 billable?

Accepted Answer

Yes. A83.5 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. A83.5 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

What is the V28 vs V24 difference for A83.5?

Accepted Answer

A83.5 does not map to a payment HCC under either the CMS-HCC V28 risk adjustment model or the older V24 model. V28 reached 100% phase-in for payment year 2026, replacing V24 which was used during the PY2024–PY2025 transition. Because neither model rewards A83.5 with a risk adjustment factor, it contributes zero to a Medicare Advantage beneficiary's RAF score in either version. Coders should check whether provider documentation supports a more specific child code that does map to a payment HCC.

Question 5

What should coders know when reporting A83.5?

Accepted Answer

Verify the specific type of encephalitis documented in the medical record, as California encephalitis is a specific arboviral infection distinct from other encephalitis types Look for documentation of the acute phase and any residual neurological effects, as these may require additional codes for sequelae if the patient has long-term complications

A83.5

Is A83.5 an HCC code?

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