A51.0
BillablePrimary genital syphilis
Last updated: FY2026 ICD-10-CM (Oct 1, 2025 – Sep 30, 2026) | CMS-HCC V28 (100% phase-in, PY2026)
Is A51.0 an HCC code?
No. A51.0 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
A51.0 is the ICD-10-CM diagnosis code for primary genital syphilis. This is the initial stage of syphilis infection that appears as a painless sore or ulcer on the genitals, typically occurring 3-90 days after exposure to the bacteria. It is the first sign of syphilis infection and is highly contagious. A51.0 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).
A51.0 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.
Ensure the syphilis is documented as primary stage and specifically affecting the genital area to distinguish from secondary or latent syphilis.
HCC Buddy maintains structured V28 and V24 mapping, RAF weights, and MEAT documentation criteria for A51.0 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
- •Ensure the syphilis is documented as primary stage and specifically affecting the genital area to distinguish from secondary or latent syphilis
- •Verify that serological testing (RPR/VDRL or treponemal tests) results are documented in the medical record to support the diagnosis