Question 1

What is ICD-10 code A77.3?

Accepted Answer

A77.3 is the ICD-10-CM diagnosis code for spotted fever due to rickettsia australis. This is a tick-borne bacterial infection caused by Rickettsia australis, a microorganism transmitted through tick bites, primarily occurring in Australia. The infection causes fever, rash, and other flu-like symptoms. A77.3 sits in the ICD-10-CM chapter for certain infectious and parasitic diseases (a00-b99), within the section covering rickettsioses (a75-a79).

A77.3 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.

Verify documentation confirms Rickettsia australis as the causative organism; do not use this code for other spotted fever types (such as Rocky Mountain spotted fever or Mediterranean spotted fever).

Question 2

Is A77.3 an HCC code?

Accepted Answer

No. A77.3 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 A77.3 billable?

Accepted Answer

Yes. A77.3 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. A77.3 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

Which HCC does A77.3 map to under V28?

Accepted Answer

A77.3 does not map to a CMS-HCC V28 payment category. Check the current CMS-HCC V28 model file for payment year 2026 rather than an older V24 tip sheet.

Question 5

What does A77.3 pay in RAF?

Accepted Answer

A77.3 has no separately stated V28 community RAF weight. If it is not a V28 payment HCC, it adds nothing to a community RAF score.

Question 6

What is the V28 vs V24 difference for A77.3?

Accepted Answer

A77.3 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 community model rewards A77.3 with a risk adjustment factor, it contributes zero to a Medicare Advantage beneficiary's V28/V24 community RAF score in either version. Coders should check whether provider documentation supports a more specific child code that does map to a community payment HCC.

Question 7

What documentation supports A77.3?

Accepted Answer

Verify documentation confirms Rickettsia australis as the causative organism; do not use this code for other spotted fever types (such as Rocky Mountain spotted fever or Mediterranean spotted fever) Document the geographic location (Australia) and presence of tick exposure when available, as this supports medical necessity and accurate diagnosis coding A77.3 is not a CMS-HCC payment code, so MEAT is not the payment hook. Documentation still has to support the diagnosis if you report it.

HCC Buddy Code Card

A77.3

Is A77.3 an HCC code?

Get the V28 RAF + MEAT cheat sheet

What This Code Means

Coding Tips

Child Codes

Code Hierarchy

Work A77.3 in HCC Buddy

A77.3 ICD-10-CM Code: Spotted fever due to Rickettsia australis

HCC Buddy Code Card

A77.3

Is A77.3 an HCC code?

Get the V28 RAF + MEAT cheat sheet

What This Code Means

Coding Tips

Child Codes

Code Hierarchy

Work A77.3 in HCC Buddy