Define Case Mix Index (CMI) and explain its relevance to CDI metrics.

• A. CMI is the total number of admissions per month.
• B. CMI is the average DRG weight of all cases; it reflects patient complexity and drives reimbursement; CDI aims to optimize accurate DRG capture to reflect true complexity.
• C. CMI is the hospital's case mix by payer mix.
• D. CMI is the hospital's overall revenue per patient.

Answer: (B)

The concept being tested is what CMI represents and why it matters for CDI. CMI is the average DRG weight across a hospital’s discharges. DRG weights code the relative resource use and acuity of each case, so the average weight—the CMI—summarizes how complex or resource-intensive the patient mix is over a period. In DRG-based payment systems, higher weights translate to higher expected reimbursement, so the CMI serves as a gauge of overall case complexity and the financial impact of that complexity.

CDI focuses on documentation that accurately captures a patient’s diagnoses, severity, and complications. When documentation misses or undercodes true complexity, the assigned DRGs can be lighter than warranted, lowering the CMI and underestimating reimbursement. By improving documentation to reflect the true complexity, CDI helps ensure DRGs (and their weights) align with the actual resource use, making the CMI a meaningful signal of how well the hospital’s documentation supports its case mix and financial outcomes.

This concept isn’t about counting admissions, payer mix, or revenue per patient; it’s about the average DRG weight that reflects how sick or resource-demanding the patient population is and how CDI efforts influence that reflected complexity in reimbursement.