Question 1

What is ICD-10 code I00?

Accepted Answer

I00 is the ICD-10-CM diagnosis code for rheumatic fever without heart involvement. Acute rheumatic fever, an inflammatory disease that can develop after a strep throat infection, affecting joints and other tissues but not the heart. I00 sits in the ICD-10-CM chapter for diseases of the circulatory system (i00-i99), within the section covering acute rheumatic fever (i00-i02).

I00 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.

This code is used only when rheumatic fever is present without cardiac involvement; if heart involvement exists, use codes I01.0-I01.9 instead.

Question 2

Is I00 an HCC code?

Accepted Answer

No. I00 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 I00 billable?

Accepted Answer

Yes. I00 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. I00 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 I00?

Accepted Answer

I00 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 I00 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 I00?

Accepted Answer

This code is used only when rheumatic fever is present without cardiac involvement; if heart involvement exists, use codes I01.0-I01.9 instead Document evidence of preceding streptococcal infection and clinical manifestations such as polyarthritis or chorea

I00

Is I00 an HCC code?

What This Code Means

Coding Tips

Includes

Excludes 1 — Do NOT code together

Code Hierarchy

Open I00 in the Interactive Encoder