South Korea-based Mezzion Pharmaceuticals, a developer of therapies for patients with single ventricle heart disease, announced on Wednesday a positive development for the Fontan community with the introduction of new, dedicated ICD-10 diagnosis codes for Fontan-associated conditions in the US Centers for Medicare & Medicaid Services (CMS) FY 2026 IPPS Proposed Rule.

Listed under Table 6A of the proposed rule, four new diagnostic codes represent the first-ever formal classification of complications specific to the Fontan circulation: I27.840 – Fontan-associated liver disease (FALD); I27.841 – Fontan-associated lymphatic dysfunction; I27.848 – Other Fontan-associated condition; and I27.849 – Fontan-related circulation, unspecified.

These new codes are expected to allow for improved clinical documentation, insurance reimbursement and health system recognition of the unique and complex needs of patients living with Fontan physiology.

The codes create a new branch within the ICD-10 classification system specific to Fontan physiology. According to Mezzion, this advancement will help clinicians better track and manage Fontan-related complications, fuel more accurate epidemiological research and enable public and private payers to recognise Fontan patients as a distinct population with specific medical needs.

Mezzion added that the new codes mark a significant regulatory and commercial milestone in the development of udenafil, a first-in-class therapy under investigation to improve exercise capacity in Fontan patients. Udenafil is currently being evaluated in FUEL-2, a Phase 3 confirmatory trial being conducted across the United States, Europe and APAC.

The proposed ICD-10 codes are open for public comment until 10 June 2025, with finalisation expected by August 2025 and implementation anticipated by September 2025.