HCC risk adjustment errors are costing Medicare Advantage plans and ACOs millions in missed revenue and audit penalties. With the 2024 CMS-HCC V28 model now in its second full performance year, documentation gaps and coding inaccuracies remain the top drivers of compliance failures and recapture audits in 2026. This guide identifies the most common HCC risk adjustment errors tied to V28 implementation, explains how documentation deficiencies trigger audit failures, and outlines actionable prevention strategies for revenue cycle leaders managing risk-adjusted populations.
Why V28 model changes increased HCC coding error rates
The CMS-HCC V28 model introduced over 2,000 new diagnosis codes and removed 1,400 from risk scoring calculations. The model's restructured disease hierarchies changed how coexisting conditions interact, which means a diagnosis combination that scored appropriately under V24 may now trigger a hierarchy suppression or fail to capture severity.
Most coding teams trained under V24 still default to legacy documentation patterns. They don't recognize when a provider's encounter note lacks the specificity V28 demands. For example, "diabetes with complications" no longer maps uniformly. V28 requires explicit documentation of the complication type, laterality where applicable, and stage or severity descriptors.
RADV audits conducted in late 2025 showed that 38% of HCC code deletions stemmed from insufficient documentation specificity, not from outright coding errors. The documentation existed, but it didn't meet the heightened standard V28 enforces.
Common V28-specific coding mistakes
Coders frequently miss the updated mappings for chronic kidney disease. Under V28, CKD stage 3 no longer contributes to risk adjustment scoring unless combined with a qualifying comorbidity. Documentation must explicitly state both the CKD stage and the related condition within the same encounter to justify the HCC.
Behavioral health diagnoses saw significant restructuring. Depression severity levels now require documented symptom counts and functional impairment details. A note stating "major depressive disorder" without episode specification or severity qualifiers won't support the intended HCC under V28 mapping logic.
Cardiovascular conditions also shifted. Heart failure documentation must now specify both ejection fraction classification and NYHA functional class to map correctly. Notes that state "CHF, compensated" without these clinical details fail V28's documentation threshold during RADV validation.
Documentation gaps that trigger audit failures
RADV audits don't just flag incorrect codes. They delete legitimate diagnoses when supporting documentation fails to meet CMS standards. The 2026 audit cycle shows documentation issues account for 67% of all deleted HCCs, far exceeding actual coding logic errors.
The most frequent gap: missing linkage between diagnostic statements and clinical evidence. A provider documents "COPD" in the assessment, but the clinical note lacks spirometry results, symptom descriptions, or medication management details. The diagnosis exists, but the medical record doesn't prove it was evaluated or addressed during the encounter.
CMS requires that each reported diagnosis be supported by provider evaluation, assessment, or plan documented in the same face-to-face visit. Diagnoses carried forward from problem lists without current clinical context get deleted during audit. This affects chronic conditions disproportionately, since they often appear in multiple encounters without active reassessment notation.
Signature and credentials compliance
Authentication failures remain a persistent audit trigger. CMS requires that the rendering provider's signature include credentials and date. Electronic signatures must be linked to a unique user identifier that traces back to a credentialed provider.
Many EHR templates auto-populate signatures without forcing credential verification. When auditors can't confirm the signer's professional qualification, the entire encounter gets invalidated regardless of documentation quality.
Telehealth visit documentation standards
Telehealth visits expanded significantly post-pandemic, but their documentation often falls short of risk adjustment standards. CMS allows telehealth encounters for HCC capture, but the note must document the visit modality and confirm visual or verbal assessment of the reported condition.
A phone-only visit documenting "diabetic retinopathy" without notation of how the condition was assessed raises audit flags. The provider must document what clinical information supported the diagnosis during a remote encounter. For organizations managing significant telehealth volumes, implementing telemedicine documentation protocols that meet risk adjustment standards prevents downstream audit exposure.
How hierarchy suppressions create hidden revenue loss
V28 expanded the use of hierarchies to prevent duplicate scoring of related conditions. When a more severe diagnosis is documented, less severe manifestations in the same disease category get suppressed and contribute zero risk score.
The problem: coders often report both the severe and mild diagnosis without recognizing the hierarchy relationship. The claim processes without error, but only the higher-weighted HCC scores. The second diagnosis adds administrative burden without revenue benefit and increases audit risk if its documentation is weaker.
Diabetes hierarchies exemplify this. If a patient has both diabetic nephropathy (HCC 18) and uncomplicated diabetes (HCC 19), only HCC 18 scores. Reporting both codes doesn't increase reimbursement and doubles the documentation that must withstand audit scrutiny.
Revenue cycle teams should audit current coding patterns against V28 hierarchy tables. Identify diagnoses your coders routinely report together that suppress each other. Then adjust coding workflows to capture only the highest-severity supported diagnosis, reducing documentation burden and audit surface area.
Missed opportunities from incomplete diagnosis capture
The inverse problem: coders under-document severity because they don't prompt providers for necessary clinical detail. A note states "peripheral vascular disease" without specifying whether it's atherosclerotic, involves claudication, or has progressed to gangrene.
Each severity level maps to a different HCC with different risk weights. Without prompting, providers document to the level sufficient for clinical care but insufficient for accurate risk capture. This isn't a coding error, it's a clinical documentation gap that CDI program support strategies address by implementing pre-encounter planning and concurrent physician queries.
Prevention strategies for reducing HCC coding errors
Error prevention starts with coder education specific to V28 changes. Generic annual training isn't sufficient. Coders need diagnosis-specific guidance on V28 mappings, particularly for the cardiovascular, renal, and behavioral health categories that saw the most significant restructuring.
Build a V28-specific reference tool that maps common diagnoses to their required documentation elements. When a coder encounters "heart failure," the tool should list exactly what the note must contain: ejection fraction, NYHA class, acute vs chronic specification, and medication management notation. This converts V28's complexity into an actionable checklist.
Implement pre-coding documentation review for high-value diagnoses. Before coding an encounter with suspected HCC conditions, a trained abstractor reviews the note against V28 documentation standards. If gaps exist, a query goes to the provider before claim submission. This prevents the claim-query-resubmission cycle that delays revenue and frustrates physicians.
Audit preparedness protocols
Don't wait for a RADV audit notice to assess documentation quality. Conduct quarterly internal audits using CMS's published RADV methodology. Pull a random sample of coded encounters, apply the same validation standards CMS uses, and calculate your projected deletion rate.
If internal audits show deletion rates above 15%, you have a systematic documentation or coding issue that will cost significant revenue during formal audit. Address root causes before CMS comes calling.
Track denial and deletion patterns by diagnosis code and provider. If one physician's heart failure diagnoses consistently fail validation while others' don't, that's a targeted education opportunity. If all coders struggle with a specific diagnosis category, that indicates a gap in your coding reference materials or training curriculum.
Technology and workflow integration
Modern EHR systems can enforce documentation completeness before note closure. Configure templates to require specific data elements when a provider selects an HCC-eligible diagnosis. If a provider documents diabetes with neuropathy, the template shouldn't allow note signing until the neuropathy location and severity are specified.
These hard stops frustrate providers initially, but they prevent the documentation gaps that cost real revenue. Frame the requirement as audit protection, not administrative burden.
For organizations with risk adjustment and HCC coding programs spanning multiple facilities or specialties, centralized coding oversight prevents inconsistent interpretation of documentation standards. A single coding authority reviewing edge cases and issuing guidance ensures all coders apply V28 logic uniformly.
What RADV audit trends tell us about 2026 compliance priorities
CMS's 2025 RADV audit results, published in early 2026, show a clear pattern: payers with formal CDI programs had 40% lower HCC deletion rates than those relying on coder-driven queries alone. The difference isn't coding accuracy, it's documentation quality at the point of care.
Concurrent CDI specialists identify documentation gaps while the patient is still under care and the provider can amend the record with additional clinical detail. Retrospective coder queries happen after claim submission, when providers have moved on and memory of the encounter has faded. The resulting query responses are often too generic to satisfy audit scrutiny.
Behavioral health diagnoses showed the highest deletion rates in 2025 audits, at 29%. Mental health documentation often lacks the episode specification, severity descriptors, and functional impact details V28 requires. Providers document for treatment planning, not risk adjustment, and the resulting notes can't support the HCC codes assigned.
This points to a specialty-specific education need. General CDI training doesn't address behavioral health documentation nuances. Organizations with significant behavioral health populations need dedicated resources trained in psychiatric documentation standards and V28's mental health mappings.
Frequently asked questions about HCC risk adjustment errors
What are the most common HCC coding errors under the V28 model?
The most frequent errors involve insufficient documentation specificity for chronic conditions, particularly diabetes with complications, heart failure, and chronic kidney disease. Coders also commonly miss V28's expanded hierarchy suppressions, reporting multiple related diagnoses when only the most severe should be coded. Authentication failures and lack of clinical evidence linking diagnoses to the encounter account for the majority of audit deletions.
How does CMS determine if HCC documentation supports the coded diagnosis?
CMS RADV auditors require that documentation includes a clear diagnostic statement from the provider, clinical evidence supporting that diagnosis, and proof the condition was evaluated or addressed during the face-to-face encounter. The note must be signed with credentials and dated. For chronic conditions, the documentation must show current assessment, not just problem list carryforward.
Can telehealth visits be used for HCC risk adjustment coding?
Yes, CMS allows HCC capture from telehealth encounters, but the documentation must specify the visit modality and explain how the provider assessed the reported condition remotely. Phone-only visits require clear notation of what clinical information supported the diagnosis without physical examination. Video visits need documentation of visual assessment where relevant to the condition being coded.
What happens to risk adjustment revenue when an HCC code is deleted during audit?
When CMS deletes an HCC during RADV audit, the payer must return the associated risk-adjusted payment for that diagnosis. If deletion rates exceed the contract's error threshold, CMS may extrapolate the error rate across the entire member population and demand return of proportional payments across all members, not just those audited. This can result in multi-million dollar recaptures.
How often should we audit our HCC coding for documentation compliance?
Best practice calls for quarterly internal audits using CMS RADV methodology, sampling 200-300 member records across high-risk diagnosis categories. Monthly focused audits of specific providers or diagnosis codes showing elevated denial patterns help identify issues before they become systematic. Any organization with RADV deletion rates above 10% should conduct more frequent audits until root causes are corrected.
Building sustainable HCC coding accuracy
HCC risk adjustment errors aren't random. They follow patterns tied to inadequate provider documentation, coder misunderstanding of V28 logic, and lack of concurrent review processes. Organizations that treat these as isolated mistakes will continue bleeding revenue to audits and denials.
Sustainable accuracy requires integrated CDI and coding workflows, V28-specific education for both clinical and coding staff, and systematic audit protocols that identify problems before CMS does. The 2026 compliance landscape rewards organizations that invested in these capabilities over the past two years and penalizes those still operating on V24 assumptions.
If your organization's HCC denial rates are climbing or you're preparing for upcoming RADV audits, MedCodex Health provides specialized risk adjustment coding review and CDI support designed specifically for V28 compliance. Our team helps identify documentation gaps, educate providers on HCC-specific requirements, and implement audit-proof workflows. MedCodex Health offers a complimentary coding assessment to benchmark your current accuracy against CMS standards and identify your highest-risk areas.