MS-DRG (Medicare Severity DRG)
The severity-adjusted version of the DRG system used by Medicare since 2007, expanding groupings to capture complication and comorbidity burden and refine payment accuracy.
On hospital cost-and-quality pages, MS-DRG (Medicare Severity DRG) carries a specific technical meaning that often differs from how the term is used in clinical practice or general medical writing. The definition here is the CMS-file usage. On the LakeQuality value rubric, MS-DRG (Medicare Severity DRG) is one of the inputs (directly or indirectly) to the combined cost-and-quality grade. Understanding how the term is computed at CMS — what counts and what does not — is part of reading hospital pages defensibly.
Each hospital page on LakeQuality surfaces the specific MS-DRG (Medicare Severity DRG) value for that facility (when CMS reports one), so the general definition here translates into a concrete data point on the per-hospital pages you actually use.
How It Works
MS-DRGs were introduced in Fiscal Year 2008 as a major refinement of the original DRG system. CMS split most base DRGs into two or three severity tiers: without CC/MCC, with CC, and with MCC, where CC indicates a complication or comorbidity and MCC indicates a major version. The current MS-DRG system contains approximately 750 codes organized into 25 Major Diagnostic Categories (MDCs) aligned to body systems. Severity is driven by secondary diagnoses coded on the UB-04 claim form using ICD-10-CM codes; a single additional diagnosis like acute respiratory failure or sepsis can shift a stay from a lower-weight DRG to one paying $10,000-$20,000 more. For example, DRG 291 (heart failure with MCC) has a relative weight near 1.4 and pays about $11,500, while DRG 293 (heart failure without CC/MCC) has a weight near 0.7 and pays about $5,800. Each year CMS updates MS-DRG weights in the IPPS final rule, recalibrating against the most recent MedPAR cost and charge data from roughly 3,300 IPPS hospitals. Hospitals closely track their case mix index (CMI), which is the average MS-DRG weight across all Medicare discharges. Academic medical centers like Johns Hopkins and UPMC typically run CMIs above 2.0, while community hospitals sit between 1.2 and 1.5. The Recovery Audit Contractor (RAC) program specifically targets upcoding between severity tiers because the dollar impact of a single shifted admission can exceed $10,000. Clinical documentation improvement (CDI) programs exist precisely to ensure physician notes support the severity level coded.
Related Terms
- Diagnosis Related Group (DRG), A classification system that groups hospital inpatient stays into categories based on diagnosis, procedures, and patient complexity, used by Medicare to determine how much a hospital gets paid.
- Case Mix Index (CMI), A measure of the average complexity and resource intensity of a hospital's Medicare patients, calculated as the average MS-DRG relative weight across discharges.
- ICD-10 Code, The International Classification of Diseases, 10th Revision, code used to identify patient diagnoses on hospital claims, replacing ICD-9 in the U.S. on October 1, 2015.
- Upcoding, The practice of assigning a higher-severity MS-DRG, ICD-10 code, or CPT code than the patient's actual condition warrants, resulting in higher Medicare or insurer reimbursement.
- UB-04 Claim Form, The standardized hospital billing form (also called CMS-1450) used by hospitals and other institutional providers to bill Medicare, Medicaid, and commercial insurers for facility services.
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About This Definition
This definition is part of the HospitalCostData Hospital Pricing Glossary, 47 terms explaining hospital costs, quality ratings, and healthcare billing. Written for patients, journalists, researchers, and healthcare professionals.