A64
BillableUnspecified sexually transmitted disease
Last updated: FY2026 ICD-10-CM (Oct 1, 2025 – Sep 30, 2026) | CMS-HCC V28 (100% phase-in, PY2026)
Is A64 an HCC code?
No. A64 is a billable ICD-10-CM code but does not map to any HCC category in V28, V24, ESRD, or RxHCC.
This code does not map to an HCC category in any model (V28, V24, ESRD, RxHCC).
What This Code Means
A64 is the ICD-10-CM diagnosis code for unspecified sexually transmitted disease. This code is used when a patient has a sexually transmitted infection, but the specific type has not been identified or documented. It serves as a placeholder diagnosis when the exact STI is unknown or testing results are pending. A64 sits in the ICD-10-CM chapter for certain infectious and parasitic diseases (a00-b99), within the section covering infections with a predominantly sexual mode of transmission (a50-a64).
A64 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 the specific STI cannot be determined; always attempt to identify the causative organism through testing and documentation before assigning this unspecified code.
HCC Buddy maintains structured V28 and V24 mapping, RAF weights, and MEAT documentation criteria for A64 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
- •Use this code only when the specific STI cannot be determined; always attempt to identify the causative organism through testing and documentation before assigning this unspecified code
- •Review the medical record for any test results, cultures, or provider notes that might specify the type of STI, as using a more specific code improves clinical clarity and treatment tracking