HCC Buddy

CMS fully rolled out the V28 HCC risk adjustment model effective January 1, 2026. If your team is still coding against V24 intuitions or working from outdated reference materials, you're not just slower — you may be miscoding risk scores in ways that will surface in RADV audits.

This guide covers what actually changed in V28, how to identify affected codes quickly, and what your workflow needs to look like now that V28 is the operative standard.

What Is the V28 HCC Model?

The CMS Hierarchical Condition Category (HCC) model is the risk adjustment methodology used in Medicare Advantage, ACO REACH, and other CMS value-based programs. It maps ICD-10-CM diagnosis codes to condition categories (HCCs) that predict beneficiary health costs. Higher HCC totals produce higher RAF scores and higher premium payments to plans and providers.

CMS updates the HCC model periodically to better align with clinical evidence and ICD-10-CM code changes. The V28 model, announced in the 2024 Medicare Advantage and Part D Final Rule, represents the most significant revision since the model was introduced.

V28 was phased in during 2024–2025 and is now fully operative for 2026 payment year. CMS is applying it at 100% weight — there is no more blended V24/V28 calculation.

Key Structural Changes in V28

1. Model Expanded from 86 to 115 HCC Categories

The V28 model added 29 new HCC categories, primarily to improve differentiation among high-cost conditions. Some existing categories were split to better reflect clinical and cost heterogeneity. The additions are concentrated in:

• Cardiovascular conditions (more granular heart failure staging)
• Diabetes complications (finer distinctions between complication types)
• Mental health and substance use disorders
• Neurological conditions
• Oncology (expanded cancer differentiation)

2. Over 2,000 ICD-10-CM Codes Removed from HCC Mapping

CMS eliminated thousands of diagnosis codes from HCC mapping — meaning those codes no longer count toward a patient's RAF score under V28. This is the most consequential change for coding teams doing retrospective review.

The removed codes fall into several patterns:

• Signs and symptoms without documented underlying diagnosis — codes like R05 (cough), R00.0 (tachycardia), and many R-chapter codes that were previously mapped are now excluded
• Manifestation codes without their etiology codes — the V28 model more strictly requires the underlying condition to be coded
• Unspecified codes in categories now requiring specificity — CMS pushed coders toward more specific code selection
• Certain chronic condition codes with insufficient clinical evidence for cost prediction

3. Hundreds of Codes Reassigned to Different HCC Categories

Many codes that previously mapped to one HCC now map to a different one — sometimes higher RAF weight, sometimes lower. The reassignments are not intuitive and cannot be inferred from the V24 mapping. Coders must look them up code by code.

4. RAF Weights Recalibrated

Even for codes that stayed in the same HCC category, the RAF weights for those categories changed. A V24 RAF of 0.327 for a given HCC may be 0.289 or 0.411 under V28. The category label is not sufficient — actual RAF values need V28 sources.

High-Impact Code Changes: Examples

Note: This table shows illustrative examples. Always verify current mapping against the official 2026 CMS V28 model files or a V28-aware lookup tool.

What This Means for Your Coding Workflow

1. V24 Memory Is Unreliable Now

Coders who built strong intuition for V24 HCC mapping have an advantage in knowing which conditions matter for risk adjustment — but the specific HCC categories and whether a code maps at all are no longer safe assumptions. A code that "always" mapped in V24 may be deleted in V28.

Every HCC-relevant code needs a V28 verification step. This is not optional during 2026 retrospective reviews.

2. Your QA Checklists Need Updating

If your team uses a manual QA checklist or reference list of "common HCC codes," that list needs a V28 audit. Items to verify for each code on your internal lists:

• Does this code still map to an HCC in V28? (Many were deleted)
• Which V28 HCC category does it map to? (May have changed)
• What is the current V28 RAF weight for that category?
• Are there more specific codes that capture the same condition with better V28 mapping?

3. Specificity Is More Important Than Ever

V28 removed many unspecified codes from HCC mapping. Where coders previously might have accepted an unspecified code when documentation was vague, the V28 model creates a financial incentive to push for appropriate clinical specificity in the source documentation. If a chart legitimately supports a more specific diagnosis, coders should query for it.

4. Drug-to-Diagnosis Bridges Are More Critical

Several medication classes — particularly for diabetes management, cardiovascular conditions, and immunosuppressives — are associated with HCC-relevant diagnoses that are now required to be coded with greater specificity under V28. When a patient is on insulin or specific cardiac medications, verify that all associated diagnoses are coded to the appropriate V28 specificity level.

How HCC Coders Are Adapting

The teams managing V28 transition most effectively share several characteristics:

1. They verify V28 mapping at the point of coding — not from memory or cached reference lists. Every HCC-relevant code gets a live lookup.
2. They use V28-native tools — tools that show the V28 HCC category and V24-to-V28 delta without requiring manual cross-referencing. PDF mapping tables are too slow for production coding workflows.
3. They've updated their MEAT documentation criteria knowledge — V28 specificity requirements mean MEAT criteria documentation needs to be detailed enough to support specific (not unspecified) codes.
4. They have a process for flagging changed codes — when a coder looks up a code and sees it changed between V24 and V28, that should trigger a documentation review to confirm the more specific V28 code is appropriate.

V28 and RADV Audit Exposure

CMS RADV (Risk Adjustment Data Validation) audits examine whether diagnosis codes on claims are supported by medical record documentation. V28 adds complexity to this: a code that was valid under V24 may still be clinically appropriate but no longer map to an HCC under V28, affecting risk score calculations.

For retrospective chart review, ensure your QA process distinguishes between:

• Codes that are clinically valid but no longer HCC-mapped (documentation may still be fine, but risk score contribution is zero)
• Codes where the V28 mapping changed to a different HCC (revenue and audit implications differ)
• Codes where the proper V28 approach requires a more specific code that wasn't coded

Next Steps for Your Team

1. Audit your internal "HCC code lists" — any hard-coded reference lists, QA checklists, or training materials built around V24 mapping need a V28 review.
2. Verify your lookup tools are V28-native — confirm that your coders' reference tools show V28 HCC categories and flag V24-to-V28 changes. If your tools aren't showing V28 delta flags, your team is missing a key verification step.
3. Update MEAT documentation training — ensure coders understand which specificity changes matter most for your patient population and payer mix.
4. Consider a targeted retrospective review — for high-RAF conditions with significant V28 changes (heart failure, diabetes complications, CKD), a targeted pass at recent charts may identify risk adjustment opportunities your team missed during the transition.