AI in Inpatient DRG Coding

CMS introduced Medicare Severity Diagnosis Related Groups (MS-DRGs) in fiscal year 2008. Each inpatient stay goes into one group based on the principal diagnosis, significant procedures, secondary diagnoses and sometimes discharge status. Many base DRGs split into three severity tiers: with an MCC, with a CC, or with neither. Payment is roughly the DRG's relative weight multiplied by the hospital's base rate, plus adjustments. Under the official guidelines, the principal diagnosis is the condition established after study to be chiefly responsible for the admission. Many disputes come from choosing the wrong one. AI does not decide the DRG. The grouper, a deterministic piece of software, does that. AI suggests the codes the grouper uses. Computer-assisted coding systems from vendors such as Solventum (formerly 3M Health Information Systems) and Optum read history and physicals, progress notes, operative reports, discharge summaries, lab results and medication records. They then propose codes with links to the supporting text. Hospitals use them in three ways. During the stay, they show a working DRG so documentation gaps can be fixed while the patient is still in the hospital. At final coding, they speed up code assignment. Before billing, they run DRG validation, which flags high-risk patterns such as a single CC or MCC carrying the payment, questionable principal diagnosis sequencing, and diagnoses without clear clinical support. Several misconceptions are common. More codes do not automatically mean a higher DRG. In MS-DRGs the severity tier depends on whether at least one qualifying CC or MCC is present, and CC exclusion rules drop secondary diagnoses too closely related to the principal diagnosis. A code being documented also does not make it clinically valid. Payers often deny diagnoses such as sepsis, malnutrition or acute respiratory failure when the clinical indicators do not meet their criteria. Some payers also use APR-DRGs, which add four severity-of-illness and risk-of-mortality subclasses and respond differently to secondary diagnoses.