The Case Mix Group, or CMG code, is an administrative and classification tool used within the healthcare system, primarily for acute care inpatient services. These codes provide a standardized method for classifying patient episodes based on their clinical characteristics and the expected resources needed for their care. The CMG system allows health administrators to move beyond simply counting patient admissions toward a more sophisticated measure of hospital activity. It helps in understanding the complexity of patients treated in hospital settings across the country. The Canadian Institute for Health Information (CIHI) manages the methodology that assigns these codes to ensure consistency.
Defining the CMG Code
The CMG code is an alphanumeric identifier assigned to each patient’s acute care stay, grouping cases that are statistically and clinically homogeneous. This classification system, known as CMG+, aggregates inpatients based on similar diagnoses, procedures, and anticipated resource consumption. The resulting code is typically a three-character identifier that reflects the overall complexity and nature of the hospital stay.
The methodology provides a national standard for data analysis, classifying inpatient and day surgery episodes. The CMG system groups patients who are expected to use similar amounts of hospital resources, allowing for meaningful comparisons of patient populations. It is based on routinely collected data from the hospital discharge process.
The Purpose of CMG Assignment
The assignment of a CMG is a step for the standardized measurement of healthcare activity and resource intensity across acute care facilities. This classification allows health system managers to translate complex clinical data into a measurable indicator of patient needs, which is more accurate than simply looking at the number of patients treated. The CMG forms the basis for calculating a Resource Intensity Weight (RIW), which represents the relative value of resources a case is expected to consume compared to other cases.
This weighting system is integrated into funding models, where many provinces use the RIW as a component in their hospital funding formulas, supporting activity-based funding initiatives. The code acts as a standardized proxy for the cost of treating a patient, permitting fair comparison and resource distribution across diverse institutions. Hospitals use the CMG to monitor and improve the care and services they provide by better understanding the differing care requirements of their patients.
The CMG also facilitates the development of benchmarks, allowing hospitals to compare their performance, such as length of stay or cost per case, against peer institutions. It supports epidemiological studies by providing a consistent framework for grouping patients with similar medical conditions for analysis. The CMG methodology allows for accurate program planning and evaluation, enabling hospitals to predict length of stay and resource use for specific patient groups. This approach ensures that comparisons of health data across different regions and time periods remain consistent and reliable for decision-making.
Data Inputs for CMG Calculation
The assignment of a CMG is determined by a computer algorithm known as the CMG+ grouper, which processes specific data elements collected during the patient’s hospital stay. These data elements are primarily sourced from the Discharge Abstract Database (DAD), a national repository of acute care inpatient records. The process begins by assigning a case to one of over 20 Major Clinical Categories (MCCs), largely based on the patient’s Most Responsible Diagnosis (MRDx).
The MRDx is the diagnosis responsible for the greatest portion of the patient’s length of stay in the hospital. The CMG grouper then assesses whether the case should be grouped based on a significant intervention or a diagnosis, using intervention activity data from the Canadian Classification of Health Interventions (CCI). The final CMG assignment is further refined by factors that reflect the patient’s overall medical condition and resource use.
These factors include the patient’s age group and their Comorbidity Level, which accounts for the presence and severity of secondary diagnoses or complications. The Comorbidity Level is derived from clinically significant diagnoses, coded using the International Statistical Classification of Diseases and Related Health Problems (ICD-10-CA). The combination of the MRDx, procedures performed, and complexity factors like age and comorbidities dictates which CMG code is ultimately assigned to the patient’s episode of care.