Introduction

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 Identification

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.


• SAS® FORMATS
  
  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 https://www.cihi.ca/en/data-and-standards/standards/case-mix/cmg for more information. See the Case Mix Groups (CMG™) - Overview concept for more information about CMGs.


• SAS® FORMATS
  
  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.

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.


• 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.
  
  
• SAS® FORMATS
  
  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.)

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.