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.
On hospital cost-and-quality pages, ICD-10 Code 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, ICD-10 Code 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 ICD-10 Code 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
ICD-10-CM (Clinical Modification) is the U.S. adaptation of the World Health Organization's ICD-10 system, used on every hospital and physician claim to identify patient diagnoses. Implementation on October 1, 2015 was one of the most disruptive administrative transitions in U.S. healthcare history, expanding the code set from about 13,000 ICD-9 codes to approximately 70,000 ICD-10-CM codes. The expansion supports much greater clinical specificity: a single ICD-9 code for "angina" became dozens of ICD-10 codes differentiating stable angina, unstable angina, with documented coronary atherosclerosis, without, with specified coronary vessel involvement, and so on. A parallel system, ICD-10-PCS (Procedure Coding System) with about 78,000 codes, replaced ICD-9 procedure codes for inpatient procedures; CPT remains in use for outpatient and professional procedures. ICD-10-CM diagnosis codes are the primary drivers of MS-DRG assignment. The coder reviews the medical record, assigns a principal diagnosis and up to 24 secondary diagnoses, and submits them on the UB-04 claim, where the MS-DRG grouper software maps the combination to a single MS-DRG for payment. Secondary diagnoses flagged as CC or MCC can shift the stay into a higher-paying severity tier. CMS and the AMA publish annual updates in October; ICD-10-CM is updated by the Cooperating Parties (AHA, AHIMA, CMS, NCHS) with hundreds of code changes each year. Accurate ICD-10 coding is essential for reimbursement, quality reporting (HRRP, HAC, value-based purchasing), public health surveillance, and research. Coding errors or incomplete documentation routinely cost hospitals millions annually in missed severity capture or trigger RAC takebacks when severity is unsupported.
Related Terms
- CPT Code, The Current Procedural Terminology code maintained by the American Medical Association, used to identify outpatient procedures, office visits, and services on claims.
- 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.
- 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.
- 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.
- 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.
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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.