Question 1

What is ICD-10 code H21.309?

Accepted Answer

H21.309 is the ICD-10-CM diagnosis code for idiopathic cysts of iris, ciliary body or anterior chamber, unspecified eye. Fluid-filled sacs in the iris or front part of the eye that develop without a known cause, but the affected eye is not specified. H21.309 sits in the ICD-10-CM chapter for diseases of the eye and adnexa (h00-h59), within the section covering disorders of sclera, cornea, iris and ciliary body (h15-h22).

H21.309 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.

Use this code only when documentation does not clearly indicate which eye is affected; query the provider if laterality can be determined.

Question 2

Is H21.309 an HCC code?

Accepted Answer

No. H21.309 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 H21.309 billable?

Accepted Answer

Yes. H21.309 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. H21.309 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 H21.309?

Accepted Answer

H21.309 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 H21.309 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 H21.309?

Accepted Answer

Use this code only when documentation does not clearly indicate which eye is affected; query the provider if laterality can be determined. This is a less specific code; attempt to obtain laterality information to assign a more precise code.

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H21.309

Is H21.309 an HCC code?

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H21.309 ICD-10-CM Code: Idiopathic cysts of iris, ciliary body or anterior chamber, unspecified eye

HCC Buddy Code Card

H21.309

Is H21.309 an HCC code?

What This Code Means

Coding Tips

Child Codes

Code Hierarchy

Open H21.309 in the Interactive Encoder