ICD-10-CM 2026 Updates

ICD-10-CM updates for FY 2026 (effective October 1, 2025) with implications for coding, compliance, and operational readiness.

Each fiscal year, the ICD-10-CM code set is updated to reflect evolving clinical practice, new diagnoses, and to improve specificity in coding. The FY 2026 update (effective October 1, 2025) brings substantial changes in diagnoses, deletions, revisions, and guidelines clarifications.

Coders, clinical documentation improvement (CDI) specialists, compliance teams, and health information management (HIM) departments must be aware of and prepare for these changes to ensure accurate capture of diagnoses, avoid reimbursement issues, and maintain regulatory compliance.

High-Level Summary of Changes

These changes are mandated for use for encounters (inpatient, outpatient, physician services) occurring on or after October 1, 2025.

Notable Thematic Additions & Revisions

While there are hundreds of changes, the following areas are of particular interest because of clinical impact, documentation requirements, or prevalence:

War / Military Injuries & Exposure Codes

A set of new codes addresses injuries or exposures related to war, civil insurrection, or peacekeeping operations. Examples include codes for low-level and high-level blast overpressure exposures, with initial, subsequent, and sequela designations.

Food Allergy / Immunologic Reactions

New codes expand specificity in food reactions and anaphylaxis, especially focusing on egg and milk/dairy:

• Adverse reactions to eggs (with baked egg tolerance/reactivity) across initial/subsequent/sequela categories (e.g., T78.120A, T78.121A, T78.129A, etc.)

• Anaphylactic reactions to eggs, distinguishing tolerance versus reactivity to baked egg (e.g., T78.080A, T78.081A, T78.089A)

• New allergy codes: Z91.0120 (allergy to eggs, unspecified), Z91.0121 (allergy to eggs with tolerance to baked egg), Z91.0122 (allergy to eggs with reactivity)

• Similarly, new codes for milk/dairy product reactions (e.g., T78.110A, T78.111A, T78.119A; anaphylaxis T78.070, A, etc.)

These expansions reflect evolving immunology knowledge and the need to capture more granular details about allergy phenotypes.

Mental Health / Depressive Disorders

The F32–F33 categories for major depressive disorder receive enhancements: new descriptors for severity, episode features, or other qualifiers to allow more precise coding of depressive episodes.

Injury / External Cause & Laterality

A large share of additions fall under the Injury, Poisoning & External Causes chapters (S00–T88). Many new codes allow specification by laterality, depth of injury (e.g., muscle, bone), and subtype (e.g., contusions, non-thermal blisters, nonvenomous insect bites, open wounds)

For example, some existing generic codes will be replaced with subcodes reflecting left/right laterality. This requires careful documentation to support the more specific coding. Chronic Ulcers & Skin / Subcutaneous Conditions

New codes are introduced to better define non-pressure chronic ulcers, specifying location (abdomen, neck, groin, etc.), depth (bone, muscle involvement), and staging/necrosis.

ICD-10 External Cause Codes for Medical Coding 

Social Determinants / External Factors

The Z (Factors Influencing Health) chapter is expanded in some respects — e.g., more specificity around financial insecurity (expanding on Z59.86)

Medical Coding and Billing Guidelines for Social Determinants of Health (SDOH) 

Updates to Official Guidelines for Coding & Reporting

Alongside the code set changes, the Official ICD-10-CM Guidelines for coding and reporting are updated for FY 2026.

Some areas of note:

• Clarifications around sequencing, use of “other specified / unspecified” codes, and when to code symptoms vs confirmed diagnoses.

• Adjustments to chapter-specific guidance (e.g., certain chapters may receive new precedence rules or tie-breakers).

• New or revised examples for common conditions, reflecting the new codes and best practices.

(It is advisable for coders to review the full guidelines PDF to catch all nuance changes.

2026 ICD-10-CM Guidelines 

Implementation & Operational Considerations

To ensure a smooth transition, organizations should prepare in advance. Key steps include:

1. Gap analysis & crosswalks

   • Compare existing common diagnoses to new codes and identify where documentation needs to be enhanced to support the new granularity.

   • Build crosswalk tables mapping legacy codes to new subcodes or equivalent codes.

2. Education & training

   • Train coders, auditors, billing staff, CDI teams, and clinicians (as needed) on new codes, guidelines, and documentation requirements.

   • Use “quick reference” guides for high-impact changes (e.g., allergy coding, injury laterality, ulcer staging).

3. System updates & testing

   • Update encoder/grouping/auditing tools to the FY 2026 code set and logic.

   • Perform dual coding (e.g., run both old and new code sets in parallel) during a “shadow period” before October 1, 2025, to detect issues.

   • Test claims generation, mapping to DRGs, clinical dashboards, reporting, and downstream analytic systems.

4. Clinical documentation improvement (CDI) focus

   • Engage clinicians to document laterality (left vs right), depth/severity, episode descriptors, and relevant distinctions (e.g., baked-egg tolerance) as required to support the new codes.

   • Provide a feedback loop to clinicians whose documentation falls short of supporting the full specificity.

5. Quality assurance & auditing

   • Post-go-live, monitor for increases in unspecified or “not elsewhere classified” (NEC / NOS) usage—this may indicate documentation gaps or coder unfamiliarity.

   • Audit high-volume diagnoses or those with high reimbursement risk (e.g., respiratory conditions, chronic ulcers, injury codes) for accuracy.

6. Communications & stakeholder alignment

   • Inform billing, compliance, revenue cycle, analytics, and clinical leadership of the upcoming changes and impacts.

   • Adjust internal policies, workflows, and documentation templates to accommodate new code requirements.

Risks, Challenges & Best Practices

• Documentation gaps: When clinical documentation lacks specificity (e.g., laterality, depth, episode descriptors), coders may fall back to unspecified codes—losing detail and possibly affecting reimbursements.

• Coder learning curve: 487 new codes is a substantial increase—errors are possible. Ongoing training and reference support are critical.

• System misconfigurations: If encoder systems, claims logic, or analytics aren’t updated correctly, claims denial or mapping errors may occur.

• Consistency across care settings: Outpatient, inpatient, physician, and post-acute settings must align on the adoption and interpretation of new codes and guidelines.

• Monitoring and adjustment: Post-implementation audits, performance reviews, and feedback loops will help catch errors and refine processes.

Best practices include early planning, cross-functional coordination, shadow-testing, robust training, and proactive documentation engagement with clinicians.

The FY 2026 ICD-10-CM update represents one of the more significant annual changes, with nearly 487 new, 38 revised, and 28 deleted/invalidated codes.

Because many of the new codes add granularity (laterality, severity, episodes, etc.), documentation and coder readiness will be essential to leverage the update fully. Organizations that begin preparing early—through gap analyses, system updates, training, and testing—will be better positioned to minimize disruption, maintain coding quality, and ensure accurate billing and reporting.