Question 1

What is ICD-10 code Y66?

Accepted Answer

Y66 is the ICD-10-CM diagnosis code for nonadministration of surgical and medical care. A necessary surgical procedure or medical treatment was not provided to the patient when it should have been. Y66 sits in the ICD-10-CM chapter for external causes of morbidity (v00-y99), within the section covering misadventures to patients during surgical and medical care (y62-y69).

Y66 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.

Documentation must clearly establish that a required procedure or treatment was omitted or not administered.

Question 2

Is Y66 an HCC code?

Accepted Answer

No. Y66 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 Y66 billable?

Accepted Answer

Yes. Y66 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. Y66 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 Y66?

Accepted Answer

Y66 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 Y66 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 Y66?

Accepted Answer

Documentation must clearly establish that a required procedure or treatment was omitted or not administered Link this code with the condition that should have been treated to show the impact of the nonadministration

HCC Buddy Code Card

Y66

Is Y66 an HCC code?

What This Code Means

Coding Tips

Excludes 1, Do NOT code together

Code Hierarchy

Open Y66 in the Interactive Encoder

Y66 ICD-10-CM Code: Nonadministration of surgical and medical care

HCC Buddy Code Card

Y66

Is Y66 an HCC code?

What This Code Means

Coding Tips

Excludes 1, Do NOT code together

Code Hierarchy

Open Y66 in the Interactive Encoder