Note from the ACDIS Director: Case-mix index: Use with caution

by Brian Murphy

Many CDI managers use case-mix index (CMI) as the primary metric for determining the success or failure of their program. If the CMI rises in a given month, the CDI staff is doing its job, appropriately querying physicians for the correct principal diagnosis and accompanying complications/comorbidities. If the CMI dips, CDI staff aren’t getting physicians to respond, or aren’t reviewing records thoroughly enough.

Or so goes the common logic.

But using CMI as your solitary or even principal metric for success is fraught with problems. Sure, CMI shows a good snapshot of the type of patients a hospital is treating. But as a cold piece of data in isolation it does not tell the story of what is going on inside  the walls of a given facility. For example, what happens if a high-volume heart surgeon in your hospital takes two weeks’ vacation this summer? Your CMI will dip, perhaps significantly if you work in a small facility. What happens if your   hospital adds an expensive new neurosurgery service line? Your CMI is going to climb. And both of these factors are out of the hands of CDI. Is this the measure you ultimately want to be judged against?

Glenn Krauss, BBA, RHIA, CCS, CCS-P, CPUR, FCS, PCS, C-CDIS, CCDS an independent revenue cycle consultant from Madison, Wis., and a member of the ACDIS advisory board, has uncovered another problem with CMI as a CDI metric: It doesn’t account for takebacks from Recovery Auditors (commonly known by their original acryonym RACs), Medicare  Administrative Contractors (MACs), and other audit entities.

Krauss refers to CMI “as the cost to buy the product. We should be using gross margin, instead of CMI. Gross margin is gross increase in case mix—minus the take-backs.That’s the net benefit.”

Krauss cites a New England hospital currently under scrutiny as part of an Office of the Inspector General study. An auditor is reviewing more than 100 records of DRG 252, Other vascular procedures with MCC. These records were selected primarily for the fact that they contained only one MCC.

In many of these charts encephalopathy was written only once in the chart, and without the necessary consistency or continuity.

“Undoubtedly, these MCCs will ultimately be denied by the reviewer,” Krauss says. The result is an artificially high CMI that will come back down. “What is the net benefit if we don’t solidify the chart to remain accurate?” Krauss asks.

Instead of declaring victory after a query results in documentation of a single shaky CC or MCC, Krauss says CDI specialists should pursue “valid and explicit, well orchestrated documentation throughout the chart.” This solidifies the entire chart and ultimately results in a more accurate CMI.

In short, CDI departments shouldn’t ignore CMI. But if you do use it, make sure you account for other contributing factors. Deduct valid auditor recoupments from your numbers. And strive in your efforts to create a strong chart, top to bottom, that can withstand scrutiny. Doing so ensures that your CMI is a true reflection of severity of illness—and not an easy auditor target.

Editor’s Note: This article was originally published in the July 2012 edition of the CDI Journal. Murphy is the director of ACDIS. Contact him at bmurphy@acdis.org.