HCC Risk Adjustment Coding: A Complete Guide for Coders

Risk adjustment predicts how much care a population is expected to need, so that health plans enrolling sicker people are paid more than plans enrolling healthier people. In Medicare Advantage (MA), CMS does this with the CMS Hierarchical Condition Category (CMS-HCC) model. Diagnosis codes are the raw material — which is why HCC coding is both valuable and closely audited.

How does the CMS-HCC model work?

1. Providers document and code diagnoses from qualifying encounters.
2. Diagnosis codes are mapped to HCCs — groups of clinically related conditions with similar expected cost. Many diagnosis codes map to no payment HCC at all.
3. Hierarchies keep only the most severe HCC within a related family (for example, a more severe form of a disease supersedes a less severe one).
4. Each HCC has a coefficient. Coefficients for HCCs, demographic factors (age, sex, Medicaid status, disability, institutional status) and certain disease interactions are added together.
5. The total is the beneficiary's risk adjustment factor (RAF) score, which scales the plan's payment.

Risk scores are prospective: diagnoses from one calendar year generally inform payment for the following year. That is why conditions must be documented and coded every year — a chronic condition not captured in a year does not count for the next.

What changed between V24 and V28?

CMS introduced a revised model, commonly called V28, for payment year 2024 and phased it in over three years:

V28 reorganized the categories (increasing the number of payment HCCs from 86 to 115), recalibrated coefficients on more recent data, and removed many diagnosis codes from payment HCCs — particularly codes CMS considered discretionary or poorly predictive. Some conditions that once added to the RAF no longer do; others now distinguish severity more finely.

What documentation supports an HCC?

Risk adjustment diagnoses must come from a face-to-face (or qualifying telehealth) encounter with an acceptable provider type, and must be documented in the record for that date of service. Coders apply the ICD-10-CM Official Guidelines — for outpatient encounters, code conditions that exist at the time of the encounter and require or affect patient care, treatment or management.

Many organizations use the MEAT convention (Monitor, Evaluate, Assess/Address, Treat) as an internal test of whether the record shows a condition was actually addressed. MEAT is an industry practice, not a CMS rule — but it reflects what auditors look for: evidence in the note, not just a problem-list entry.

What is RADV?

Risk Adjustment Data Validation (RADV) audits are CMS's main tool for checking whether diagnoses submitted by MA plans are supported by medical records. Unsupported HCCs can lead to payment recovery. RADV methodology — including extrapolation of error rates to contract-level payments — has been the subject of rulemaking and litigation, so always check CMS for the current status before advising on exposure.

Best practices for HCC coders

Key takeaways