Health Information Management

Membership Update: Case mix index quandary

CDI Strategies, April 16, 2015

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Many programs evaluate their facility’s case mix index (CMI) on a regular basis, and many (for good or ill) use this metric as evidence of a CDI program’s success or shortcomings. Finance departments consider CMI when determining the hospital’s budget. If the hospital’s actual CMI is less than what the finance department predicted, the hospital may experience a loss in revenue. Even seemingly small changes in CMI have a large effect on the hospital’s bottom line.

To calculate CMI, choose a time period (e.g., monthly, quarterly, or annually) to examine. Within that time, take all the DRGs billed and add up the relative weights (RW). Now, divide that number by the total number of DRGs. What you are left with is your hospital’s CMI for that month.

If your CMI drops, it could be a sign of change in surgical or medical volumes, for example. Similarly, if your hospital’s CMI is lower than hospitals in your area, it could be a sign that the hospital is not capturing the complications and comorbidities (CC) and major CCs (MCC) that group those accounts into a higher-weighted DRG.

Many facilities actually created CDI programs for the singular reason to improve their CMI (read CDI programs drive up case mix index, revenue), hiring large staff in order to dramatically shift the numbers through improved CC/MCC capture.

However, measuring the change in your CMI as a prime indicator of your CDI program’s success can potentially damage your hospital, Robert S. Gold, MD, founder of DCBA Inc., in Atlanta, wrote in the CDI Journal article “Avoid the CMI trap: Measure your CDI program using severity-adjusted data.”

“CMI is a measure of who walks through the door, and, on a daily, weekly, or monthly basis, physicians in your hospi­tal treat a different mix of patients. For example, if your heart surgeon takes a vacation, your CMI will drop. If a physician performs three tracheostomies one month, and not the next, your overall CMI will fall,” Gold wrote.

Recently, the CDI Talk community raised the question of investigating the CMI again. Having seen a dramatic CMI drop at one facility, hospital administrators turned to their CDI program coordinator to find out why. After doing some digging in to the data, evaluating the CMI over time by service line, she determined a decrease in cardiac and orthopedic surgeries.

The group additionally opined that increases in observation services or outpatient treatments could contribute to reductions in CMI, and that, with ongoing emphasis on healthcare quality and keeping patients out of the hospital, such CMI shifts may continue. The group also worried about the effect of ICD-10-CM/PCS on CMI, as the healthcare universe adjusts to the shift in the code sets.

As in the CDI Talk case above, tracking the CMI can yield some pretty interesting information and highlight business opportunities for the hospital overall. CDI programs focused on CMI improvement, however, face the perennial risk of incentivizing staff to quickly capture that MCC and move on to the next record in search of buried documentation financial returns. And that, of course, can lead to non-compliant behaviors, wreak havoc with medical staff support of CDI efforts, and possibly lead to claims denials on the other end of the process.

Editor’s Note: The previous information was compiled from a variety of ACDIS resources to illustrate how members can access a range of information and guidance on a given topic. For additional information, visit the ACDIS Forms & Tools Library, the CDI Roadmap, or review the following articles:



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