Major diagnostic category
The MDC is not a diagnosis code. Diagnosis codes are ICD-10-CM. The grouper uses those codes, among other inputs, to pick the MS-DRG.
Source: CMS-1849-CN, Table 5, file dated September 23, 2026.
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Definition · Codes and claim data
Major diagnostic category
A major diagnostic category is the broad body-system group that contains a set of MS-DRGs. Table 5 of the FY2027 IPPS correction notice lists the MDC next to the group when the file has one. Pre-MDC groups, including transplants and tracheostomy, sit outside a single body system. The lookup is at /drg.
Questions
Major diagnostic category, answered
Is an MDC an ICD-10-CM code?
No. An MDC is a grouper category. ICD-10-CM codes are inputs to the grouper, not the MDC itself.