Concept: Surgical/Medical Outpatient Identification
Last Updated: 2003-06-09
This concept discusses the methods used at MCHP to identify surgical and medical outpatient cases that can then be used for further analyses. In general, the Transaction Code (TRANSACT='3' or '5') or Admission Status (ADSTAT='4') is used to identify the outpatient cases, and then one of three different methods can be used to identify the surgical/medical groups, based on Diagnosis Related Groups(DRGs™), Day Procedure Groups (DPGs™), or International Classification of Disease (ICD-9-CM) codes.
Note: Outpatient surgery is also called day surgery. Please see the updated concept related to this concept titled Day Surgery Hospitalizations .
Note: As of April 2001, the removal/biopsy of lumps and bumps has been removed from the required codes for recording day surgery events in the HAUM. This is mostly ICD-9-CM procedure code 863 but also 861, 862 (associated with tariff code 0253 (0254 0116 0112); 253 is Excision and simple closure). This causes a very significant decrease in day surgery events as defined by DRG and possibly DPG. (added June 2003)
Outpatient cases are identified in the Hospital Discharge Abstracts data using either the Transaction Code that indicates an outpatient or day care surgery case, or by the Admission Status indicating day surgery. The Transaction Code is an "in-house" variable created to identify inpatient, outpatient, day care surgery, and stillborn cases.
In Manitoba, hospitals are not required to submit a hospital discharge abstract for all medical outpatients. This means that only surgical outpatients are consistently defined in the abstracts data.
Method 1 - Identifying Surgical/Medical Outpatients Using DRGs
Since 1989, DRGs (Diagnosis Related Groups) and related codes have been assigned to each case in the Hospital Discharge Abstracts data, based on ICD-9-CM diagnosis and procedure codes.
- For more information about DRGs, see the concept Diagnosis Related Groups (DRG) Overview.
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 SAS® format: 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.
NOTE: Although DRGs are not strictly designed for use with outpatient cases, they do provide a reasonable method of identifying surgical / medical outpatient cases.
Method 2 - Identifying Surgical Outpatients Using DPGs
DPGs (Day Procedure Groups) are assigned to each appropriate outpatient case in the Hospital Discharge Abstracts data. DPGs are an extension of Case Mix Groups (CMGs) used for identifying outpatient or day surgery cases, based on the grouping methodology defined by the
Canadian Institute for Health Information (CIHI).
See the concept titled
Case Mix Groups (CMG™) - Overview
for more information about DPGs.
Additional information on Day Procedure Groups (DPGs) is available from CIHI's Web Site at: https://www.cihi.ca/en/data-and-standards/standards/case-mix/day-procedure-groups-dpg .
Method 3 - Identifying Surgical Outpatients 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 surgical outpatient cases, a DRG proxy was developed that uses ICD-9-CM procedure code.
An ICD-9-CM procedure code was considered surgical if over five years of Manitoba outpatient hospital discharge abstracts (91/92 to 95/96) it was most likely associated with a surgical DRG, otherwise it was considered medical.
A large majority of ICD-9-CM outpatient procedures were either exclusively surgical or medical or had at least a 10 to 1 ratio in favour of either.
The DRG ICD-9-CM "crosswalk" is implemented in a SAS format which categorizes a 4 digit ICD-9-CM outpatient procedure as either 'S'urgical,'M'edical, or 'X' unknown. When evaluated against the gold standard of DRG, the format was able to identify surgical and medical outpatient with at least 96% accuracy in any one year between 91/92 and 95/96.
- See ICD-9 / DRG Crosswalk from the "Health Reform in Three Provinces: A Comparative, Longitudinal Study" for more information on this method. Health Reform in Three Provinces: A Comparative, Longitudinal Study - Web Page - (Internal Access Only).
MCHP uses SAS® formats to assist in the identification of surgical cases. These formats identify the surgical/medical/other designation for each case. The format used in this project is available for downloading.
DOWNLOAD : Outpatient Surgical/Medical format - surgmed.txt
CAUTION: This format was designed specifically to identify outpatient surgical cases for this project.
NOTE: A similar crosswalk was created to identify inpatient surgical and obstetrical cases for this project. (see Method 3 in the concept titled Identifying Obstetrical / Surgical Inpatients Using ICD-9-CM Codes).
- Case Mix Groups (CMG™) - Overview
- Cataract Surgery
- Day Surgery Hospitalizations
- Diagnosis Related Groups (DRGs™) - Overview
- Surgical/Medical/Obstetrical Inpatient 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