The case mix index (CMI) is a common metric used to evaluate the return on investment (ROI) from a CDI department. However, it is a very broad metric that is affected by more than just CDI efforts. In its simplest form, the CMI represents the complexity of the patient population, which, in turn, represents revenue.
Each MS-DRG has an associated relative weight (RW), the factor upon which an organization’s payment is based. CMS introduced the concept of severity within their DRG methodology beginning in 2008, when secondary diagnoses could be classified as either a CC or MCC. Therefore, the RW of an MS-DRG where an MCC is captured is significantly higher than the relative weight of an MS-DRG without a CC or MCC. This is why CMI (i.e., the average RW for a population over a period of time) is often used to measure the success of a CDI department. The assumption is a CDI specialist will increase the volume of cases where a CC or MCC is reported, resulting in reporting claims with a higher RW, ultimately resulting in a higher CMI.
Although CDI efforts can positively affect CMI, the CDI department’s success can only be accurately represented if all other variables remain constant. Since the RW also varies by type of MS-DRG (i.e., medical vs. surgical), an organization that performs a high volume of surgeries will have a higher CMI compared to an organization that doesn’t perform many surgeries. The type of surgeries performed also affects CMI. For example, organ transplants are very complex surgeries, so they are associated with a very high RW. As another example, depending on the size of the organization, if all the cardiothoracic surgeons attend a conference for a week, say, the organization’s CMI would likely drop due to the loss of those surgical claims.
Editor’s Note: This excerpt comes from the recently published book, The Complete Guide to CDI Management, by Cheryl Ericson, MS, RN, CCDS, CDIP, Stephanie Hawley, RN, BSN, ACM, and Anny Pang Yuen, RHIA, CCS, CCDS, CDIP.
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