Term: Atypical Patient

Glossary Definition

Last Updated: 2026-01-21

Definition:

In case mix classification systems, patients are categorized as typical or atypical based on several criteria. An atypical patient is one where the hospitalization involves a transfer, sign-out against medical advice, ends in death, or has a length of stay beyond the trim point (outlier). An atypical patient has a different resource use within the hospital relative to a typical patient. Both the DRG™ and CMG™ patient case mix classification systems distinguish between typical and atypical patients. For more information please see the term typical patient .

In earlier studies cited below, hospital stays which included non-acute days had been categorized as atypical, but under current CIHI practice (exemplified by the AHS report linked below) non-acute days are not sufficient to categorize a patient as atypical.

Related concepts 

• Case Mix Groups (CMG™) - Overview
• Diagnosis Related Groups (DRGs™) - Overview

Related terms 

• Case Mix Groups (CMG™)
• Diagnosis Related Group (DRG™)
• Diagnosis Related Groups (DRG™) Weights
• Intensity of Resource Use (IRU)
• Refined Diagnosis Related Groups (RDRG®)
• Relative Case Weights (RCW)
• Trim Point
• Typical Patient

Links 

• 2022-2025 AHS Public Performance Measure Definitions, p. 29, Exclusions, Atypical cases

References 

• Brownell M, Roos NP. Monitoring the Winnipeg Hospital System: The Update Report 1993/1994. Winnipeg, MB: Manitoba Centre for Health Policy and Evaluation, 1996. [Report] [Summary] (View)
• Lloyd M, Shanahan M, Brownell M, Roos NP. Hospital Case Mix Costing Project 1991/92: Methodological Appendix. Winnipeg, MB: Manitoba Centre for Health Policy and Evaluation, 1995. [Report] [Summary] (View)
• Shanahan M, Lloyd M, Roos NP, Brownell M. Hospital Case Mix Costing Project 1991/92. Winnipeg, MB: Manitoba Centre for Health Policy and Evaluation, 1994. [Report] (View)

Term used in 

• Finlayson G, Reimer J, Dahl M, Stargardter M, McGowan K. The Direct Cost of Hospitalizations in Manitoba, 2005/06. Winnipeg, MB: Manitoba Centre for Health Policy, 2009. [Report] [Summary] [Additional Materials] (View)