Question 1

What is ICD-10 code N80.521?

Accepted Answer

N80.521 is the ICD-10-CM diagnosis code for superficial endometriosis of the sigmoid colon. Endometrial tissue grows in the sigmoid colon at a superficial level, affecting only the outer layers of the bowel wall. N80.521 sits in the ICD-10-CM chapter for diseases of the genitourinary system (n00-n99), within the section covering noninflammatory disorders of female genital tract (n80-n98).

N80.521 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.

Superficial endometriosis indicates involvement limited to the mucosa and submucosa layers.

Question 2

Is N80.521 an HCC code?

Accepted Answer

No. N80.521 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 N80.521 billable?

Accepted Answer

Yes. N80.521 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. N80.521 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 N80.521?

Accepted Answer

N80.521 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 N80.521 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 N80.521?

Accepted Answer

Superficial endometriosis indicates involvement limited to the mucosa and submucosa layers Distinguish from deep endometriosis (N80.522) which penetrates into the muscularis or beyond

N80.521

Is N80.521 an HCC code?

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Open N80.521 in the Interactive Encoder