Max Rady College of Medicine
Concept: Surgical/Medical/Obstetrical Inpatient Identification
Last Updated: 2007-10-16
This concept discusses the methods used at MCHP to identify surgical, medical and obstetrical inpatient cases that can be used for further analyses. In general, a Transaction Code is used to identify the inpatient cases, and then one of three different methods can be used to identify the surgical/medical/obstetrical groups, based on Diagnosis Related Groups (DRGs), Case Mix Groups (CMGs), or International Classification of Disease(ICD-9-CM) codes.
Inpatient cases are identified in the Hospital Discharge Abstracts data using the Transaction Code that indicates an inpatient case. The Transaction Code is an "in-house" variable created to identify inpatient, outpatient, day care surgery, and stillborn cases.
Method 1 - Identifying Surgical/Medical Inpatients Using DRGs
DRGs are assigned to each inpatient case in the Hospital Discharge Abstracts data, based on ICD-9-CM diagnosis and procedure codes recorded in each abstract. See the concept DRG (Diagnosis Related Groups) Overview for more information about DRGs.
MCHP uses SAS® formats to assist in the identification of medical/ surgical cases. These formats identify the surgical / medical designation for each DRG code value. An example of a format is available for downloading. This format is based on information from the Diagnosis Related Groups (DRG) Definitions Manual (version 13.0).
- Download : DRG Surgical/Medical Formats -- drg13sm.txt
CAUTION: Several formats exist, each one designed specifically for the corresponding DRG version (year) used to code the abstract file. Ensure that you are using the appropriate format.
Method 2 - Identifying Surgical/Medical Inpatients Using CMGs
CMGs are assigned to each inpatient case in the Hospital Discharge Abstracts data, based on ICD-9-CM and ICD-10-CA and CCI diagnosis and procedure codes recorded in each abstract. The medical / surgical designations for each CMG are based on the grouping methodology defined by CIHI. See the CIHI web site - CMG+ at
for more information. See the
Case Mix Groups (CMG™) - Overview
concept for more information about CMGs.
MCHP uses SAS® formats to assist in the identification of surgical/medical cases. These formats identify the surgical/medical designation for each CMG code value. An example of a format is available for downloading. This format is based on information from the CMG (Case Mix Group) 1995 Directory from CIHI.
CAUTION: Several format exist, each one designed specifically for the corresponding CMG version (year) used to code the abstract file. Ensure that you are using the appropriate format.
Method 3 - Identifying Obstetrical/Surgical Inpatients Using ICD-9-CM Codes
This method was used in the project Health Reform in Three Provinces: A Comparative, Longitudinal Study. Since Manitoba was the only province in this study that had Diagnosis Related Groupers (DRGs) to identify Inpatient Surgical/Obstetrical cases, a DRG proxy was developed that uses ICD-9-CM procedure and diagnosis codes to identify surgical and obstetrical DRGs respectively. ICD-9-CM diagnosis and procedure codes are stored in each inpatient case in the Hospital Discharge Abstracts data.
An ICD-9-CM diagnosis code was considered obstetrical if over five years of Manitoba inpatient hospital discharge abstracts (91/92 to 95/96) it was most likely associated with an obstetrical DRG.
- An ICD-9-CM procedure code was considered surgical if over five years of Manitoba inpatient hospital discharge abstracts (91/92 to 95/96) it was most likely associated with a surgical DRG.
The obstetrical diagnosis format was able to identify all (100%) of obstetrical DRGs in any one year between 91/92 and 95/96.
The surgical procedure format was able to identify at least 96% of surgical DRGs in any one year between 91/92 and 95/96.
When implemented together, the obstetrical and surgical formats were able to identify obstetrical/surgical DRGs with at least 99% accuracy in anyone year.
See ICD-9 / DRG Crosswalk from the Health Reform in Three Provinces: A Comparative, Longitudinal Study for more information.
MCHP uses SAS® formats to assist in the identification of obstetrical/surgical cases. These formats identify the obstetrical/surgical designation for each case. The formats used in this project are available for downloading.
Download : Obstetrical Inpatient format -- inobst.txt
Download : Surgical Inpatient format -- insurg.txt
CAUTION: These formats are designed specifically to identify obstetrical / surgical inpatients for this project.NOTE: A similar crosswalk was created to identify surgical / medical outpatients for this project. (see Method 3 in the concept Identifying Surgical / Medical Outpatients Using ICD-9-CM Codes.)
A large majority of inpatient ICD-9-CM diagnoses and procedures were either strictly obstetrical/surgical/other or were at least a 10 to 1 ratio in favour of any one category. These two crosswalks of DRG to ICD-9-CM Diagnosis and DRG to ICD-9-CM Procedure are implemented in SAS as 2 formats.
Method 4 - Identifying Medical Patients Using Service Codes
In some studies, primary service codes are used to identify inpatients staying in medical units. See the Hospital Service Codes concept for details.
SAS code and formats
- Case Mix Groups (CMG™) - Overview
- Diagnosis Related Groups (DRGs™) - Overview
- Hospital Service Codes
- Surgical/Medical Outpatient Identification
Manitoba Centre for Health Policy
Community Health Sciences, Max Rady College of Medicine,
Rady Faculty of Health Sciences,
Room 408-727 McDermot Ave.
University of Manitoba
Winnipeg, MB R3E 3P5 Canada