Core Risk Adjustment Knowledge: ICD-10-CM, HCCs, and Payment Models
This domain tests the chain from a documented diagnosis to a valid ICD-10-CM code to the risk-adjustment model that pays on it. You must know how CMS-HCC (Medicare Advantage) and HHS-HCC (ACA) models differ, and why the same code can count in one model and not another.
Coding foundations that feed the model
- Apply ICD-10-CM official guidelines: highest specificity, combination codes, Excludes1 notes, and "code also" instructions.
- Outpatient coding requires a confirmed diagnosis; "probable" or "rule out" is not coded. Laterality, type, stage, and complication must be documented.
- Only diagnoses documented and addressed in an eligible face-to-face encounter count; problem-list entries alone do not.
How HCC risk scores work
- Diagnoses map to Condition Categories and then to HCCs. Hierarchies pay only the most severe category in a family, so a diabetes-with-complications code supersedes uncomplicated diabetes.
- The risk score is the sum of demographic and HCC coefficients, normalized so the average member equals 1.0. Higher scores predict higher cost and drive payment.
- Chronic conditions must be recaptured every year; a diagnosis does not carry forward automatically.
- Medicare Advantage uses the CMS-HCC model, calculated from encounter data submitted through EDPS. RAPS is no longer used for payment.
- ACA plans use the HHS-HCC model, with separate adult, child, and infant models, and use both diagnosis and pharmacy data to calculate risk transfers among insurers.
Worked example
A 72-year-old MA member's note reads: "Type 2 diabetes with diabetic CKD stage 4; CKD stage 4." The coder assigns E11.22 and N18.4. Reasoning: the phrase "diabetic CKD" establishes causal linkage, so E11.22 is supported; N18.4 is added because the diabetes code requires "code also" to identify CKD stage. Assigning E11.9 would drop the diabetes-with-complications category and understate risk. Had the note said only "diabetes" and "CKD" with no linkage, the correct action is a query, not an assumption.
Traps that cost marks
- Coding personal history codes (Z85) as active cancer, or "history of MI" as current CAD.
- Treating every HCC as payable, ignoring hierarchies and model-specific mappings.
- Assuming a diagnosis on the problem list is billable without assessment or plan.
- Forgetting that a code valid in HHS-HCC may map differently in CMS-HCC.