CMS HCC Model V28 Changes: What Changed and What Coders Need to Know

The V28 HCC changes are not optional reading for coders working in risk adjustment, they directly affect which codes carry weight in 2026 and which do not. In 2026, the CMS HCC V28 model carries 100% of the payment weight, up from 67% in 2025. That shift means your code selections now have a bigger impact under V28 than under V24, and coders who haven't recalibrated their top-HCC priorities are leaving RAF value on the table. This post covers the 7 V28 HCC changes that most affect day-to-day work. For a complete structural breakdown of every category change, see the complete V28 reference guide.

The 2026 Blend: Why V28 Now Dominates

CMS is phasing in the V28 model over three payment years:

The practical implication: the V24/V28 blend ended after PY2025. PY2026 is scored on 100% V28, so a condition that maps in V24 but not V28 now carries zero weight. Coders must optimize entirely for V28. Your encoder, RAF calculator, and "top HCC targets" list all need to reflect the full V28 model.

The 7 V28 Changes That Most Affect Day-to-Day Coding

1. Atrial Fibrillation Now Has Its Own HCC (HCC 238)

In V28, atrial fibrillation and flutter, including I48.0, I48.11, I48.2, and I48.91, map to the new HCC 238 (Specified Heart Arrhythmias). In V24, these codes were grouped within broader cardiac categories at lower weights. The action for coders: ensure all patients with atrial fibrillation have the appropriate I48.xx code captured, not a generic cardiac NOS code that might miss the new V28 category.

2. Substance Use Disorders Now Map to HCCs (HCC 135-139)

V28 expanded the substance use disorder HCCs, which V24 already captured under HCC 54-56. These map across HCC 135-139 depending on substance and severity: alcohol dependence (F10.20) maps to HCC 139, and drug abuse such as opioid abuse (F11.10) maps to HCC 138 (mild drug use disorder, except cannabis), while alcohol abuse (F10.10) carries no HCC; the most severe presentations with psychosis map to HCC 135. The key nuance: for alcohol, only dependence maps, but for other drugs even mild use disorder can map. Verify the exact code-to-HCC assignment in the CMS 2026 model software. Many organizations that previously deprioritized behavioral health codes now need to build substance use into their capture workflows.

3. Morbid Obesity Has Its Own V28 Category (HCC 48)

E66.01 (morbid obesity due to excess calories) maps to HCC 48 in V28. In V24, obesity was grouped differently and often at lower relative weights. One important reminder: BMI Z codes (Z68.30 through Z68.39) still do NOT map to any HCC, only E66.01 carries the weight. A patient with morbid obesity documented but only a BMI Z code captured contributes nothing to RAF.

4. Chronic Kidney Disease Stage 3 Is Now Separate (HCC 329)

V28 split Chronic Kidney Disease into distinct HCC categories by stage. HCC 329 captures CKD Stage 3 unspecified and Stage 3a (N18.30, N18.31). HCC 328 captures CKD Stage 3b (N18.32). HCC 327 captures Stage 4 (N18.4). HCC 326 captures Stage 5 (N18.5) and ESRD (N18.6). This means Stage 3 Chronic Kidney Disease now contributes RAF weight independently, previously it was grouped at lower values. Stage matters more than ever in V28.

5. Diabetes Coding Requires More Specificity Than Ever

V28 uses two primary diabetes categories: HCC 37 (diabetes with chronic complications) and HCC 38 (diabetes with no, glycemic, or unspecified complications). The V24 HCC 18 and HCC 19 structure was replaced with this two-category layout. One critical V28 design decision: CMS constrained HCC 37 and HCC 38 to the same CNA coefficient (0.166). Unspecified diabetes (E11.9) maps to HCC 38 in V28 at 0.166. Diabetes with chronic complications (e.g., E11.22) maps to HCC 37, also at 0.166. The RAF contribution is identical either way because CMS deliberately equalized the weights. The lesson is still about specificity, but the reason is audit defensibility and accurate clinical representation, not a weight difference. Query for complications because the chart should reflect what the patient actually has, and because a RADV auditor will expect the documented complication to appear in the ICD-10 code.

6. Cancer Coding Is More Granular (HCC 17-24)

V28 introduced more specific cancer categories to differentiate active treatment from surveillance. Coders must use the most specific active malignancy code, not history codes (Z85.xx), for currently-treated cancer. Metastatic cancer carries a different HCC than localized cancer. Both are HCC-relevant but at different weights. If a patient is still receiving chemotherapy or radiation, the active malignancy code applies, not the history code.

7. New Disease Interaction Terms Were Added

V28 includes new disease interaction coefficients that add weight when certain HCCs co-occur in the same patient. For example, heart failure combined with Chronic Obstructive Pulmonary Disease generates an interaction term that adds to both individual HCC weights. Coders cannot directly calculate interaction terms, but they reinforce a core principle: capture ALL qualifying conditions, not just the highest-weighted one. Every additional legitimate HCC can trigger additive interaction value.

What Coders Should Do Differently in 2026

HCC Buddy shows you both V24 and V28 mappings for every code you look up, with RAF weights calculated for the correct 2026 (100% V28) model. Try it free at hccbuddy.com/encoder or see the full feature comparison at hccbuddy.com/crc.