The Code That Was Right Last Year and Wrong This Year
Clinical conditions change. A patient with well-documented CKD Stage 3 in 2024 may have progressed to Stage 4 by 2026, making the Stage 3 code inaccurate. A patient whose morbid obesity was documented during a specific encounter may have undergone bariatric surgery, making the obesity HCC unsupported. A patient whose major depressive disorder was actively managed may have achieved remission, with no current treatment documentation to support the diagnosis.
The codes submitted for these patients in prior years were legitimate when submitted. The documentation supported them at the time. But clinical reality moved forward, and the codes didn’t move with it. If CMS audits a 2024 code in 2026, they evaluate it against the documentation standard, and if the condition no longer has current management evidence, the code that was defensible when submitted becomes indefensible when audited.
This is documentation decay: the gradual erosion of a submitted code’s defensibility as clinical conditions evolve, provider documentation changes, and the original evidence ages out of relevance. It’s not fraud. It’s not even a coding error. It’s a structural consequence of submitting codes and never revisiting them.
How Decay Accumulates Into Systemic Exposure
Documentation decay compounds across a plan’s entire submitted code inventory. Each year, some percentage of previously submitted codes lose their evidentiary foundation. Conditions resolve. Providers change. Treatment plans end. Documentation emphasis shifts. The decay rate varies by diagnosis category. Chronic conditions with continuous management documentation (well-controlled diabetes, stable COPD) decay slowly. Single-occurrence acute conditions (stroke, MI) and weight-sensitive diagnoses (morbid obesity) decay faster because a single clinical change can eliminate the documentation basis.
Over three to five years of submissions without re-validation, the cumulative decay creates a significant gap between the plan’s submitted code population and the documentation that currently supports it. The plan’s risk scores reflect historical coding activity. The documentation reflects current clinical reality. The two diverge further with each passing year.
CMS’s population-level analytics can detect this divergence. When a plan’s risk scores plateau or rise while clinical complexity indicators don’t change correspondingly, the pattern suggests codes persisting beyond their documentation shelf life. That pattern invites audit attention, and the codes sampled in those audits disproportionately include the ones that decayed.
The Surveillance Solution
Post-submission surveillance is the function that catches documentation decay before auditors do. On a regular cycle, the system reviews the plan’s active HCC inventory against members’ most recent clinical documentation. Codes with current evidence are confirmed. Codes where documentation has weakened are flagged for remediation: provider outreach to refresh documentation if the condition is still active, or proactive deletion if it’s not.
The surveillance cycle should align with audit timelines. CMS now audits contracts annually. A semi-annual or quarterly surveillance cycle ensures that every submitted code has been validated against current documentation at least once within the audit window. Codes that can’t be re-validated are removed before they become audit targets.
AI makes surveillance scalable. The system compares each submitted HCC against the member’s most recent encounters, lab results, medication records, and specialist visits. Conditions with current management evidence pass. Conditions without current evidence get flagged. The coder reviews flagged codes and makes the final determination.
Managing Codes as a Living Portfolio
Retrospective Risk Adjustment Coding programs that treat submission as the end of the process are building an inventory that decays in the dark. Programs that implement post-submission surveillance treat every submitted code as an asset requiring ongoing validation, catching decay early, refreshing documentation where possible, and removing indefensible codes before they become liabilities. The distinction between these two approaches shows up directly in audit outcomes, and the plans that manage their codes as a living portfolio are the ones producing defensible results year after year.
