Question 1

What is ICD-10 code H18.539?

Accepted Answer

H18.539 is the ICD-10-CM diagnosis code for Granular corneal dystrophy, unspecified eye. It belongs to the ICD-10-CM chapter for diseases of the eye and adnexa (h00-h59). H18.539 is a billable code, meaning it can be reported on a claim as a primary or secondary diagnosis when supported by documentation. H18.539 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 H18.539 an HCC code?

Accepted Answer

No. H18.539 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 H18.539 billable?

Accepted Answer

Yes. H18.539 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. H18.539 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 H18.539?

Accepted Answer

H18.539 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 H18.539 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 H18.539?

Accepted Answer

If documentation specifies which eye is affected (right, left, or bilateral), use the more specific codes H18.531 (right eye), H18.532 (left eye), or H18.533 (bilateral) instead of the unspecified code This is a hereditary condition; verify if the patient has a family history documented, as this may support medical necessity for genetic testing or specialized ophthalmology referrals

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H18.539

Is H18.539 an HCC code?

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