Question 1

What is ICD-10 code F05?

Accepted Answer

F05 is the ICD-10-CM diagnosis code for delirium due to known physiological condition. Acute confusion and disorientation caused by a known medical condition, infection, medication, or other physical health problem, often developing suddenly. F05 sits in the ICD-10-CM chapter for mental, behavioral and neurodevelopmental disorders (f01-f99), within the section covering mental disorders due to known physiological conditions (f01-f09).

F05 is a billable ICD-10-CM code but does not map to a payment HCC under the CMS-HCC V28, V24, ESRD, or RxHCC risk adjustment models. It can be reported on Medicare Advantage encounter data submissions but it does not contribute to a beneficiary's RAF score and therefore does not affect risk-adjusted payments to the plan.

Document the specific physiological cause (e.g., infection, metabolic disorder, medication effect).

Question 2

Is F05 an HCC code?

Accepted Answer

No. F05 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 F05 billable?

Accepted Answer

Yes. F05 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. F05 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 F05?

Accepted Answer

F05 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 F05 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 F05?

Accepted Answer

Document the specific physiological cause (e.g., infection, metabolic disorder, medication effect) Delirium is typically acute and reversible; document onset and course to support this diagnosis

F05

Is F05 an HCC code?

What This Code Means

Coding Tips

Excludes 1 — Do NOT code together

Excludes 2 — Not included here, may code separately

Code First

Code Hierarchy

Open F05 in the Interactive Encoder