Concept: ICD-10 to ICD-9-CM Conversion
Last Updated: 2015-01-21
Why Convert from ICD-10 / CCI to ICD-9-CM?
Data Sets / Time Frames For Considering Conversion
PLEASE NOTE: The ICD Conversion Files developed by CIHI are available for use by researchers who have approvals to use the Hospital Abstracts data and Vital Statistics Registry data held in the MCHP Data Repository, as part of an agreement between Manitoba Health and the Canadian Institute for Health Information (CIHI). The CIHI ICD conversion files are proprietary and cannot be provided to third parties by MCHP as part of this agreement, but may be acquired directly from CIHI. For more information on the CIHI ICD conversion files, please see the following CIHI Online Store web page: Conversion Tables (for use with ICD-10-CA/CCI) or contact CIHI directly.MCHP has developed the ICD conversion tables into SAS format files. There are four format files available in the MCHP format library. Two of these format files are used for converting ICD-10 and CCI codes to the corresponding ICD-9-CM codes. The other two format files provide a "quality of fit" or grade (good/excellent, fair and poor) for each of the codes converted. The conversion formats should always be used in conjunction with the grade formats. Missing and or poor conversions (grade) will need to be checked manually or clarified with Manitoba Health/CIHI. NOTE: A great deal of valuable information is lost when translating to ICD-9-CM especially with CCI codes.
1. Converting Hospital Discharge Abstracts Diagnosis CodesAdditional Information
Since the hospital abstracts use ICD-10-CA/CCI codes, the conversion formats can be applied directly to the coded data with few or no missing values. The hospital abstracts beginning in 2004/05 now contain 25 diagnoses and 20 intervention fields.
See the SAS code below for an example of converting ICD-10 to ICD-9-CM for Hospital Separation Abstracts.2. Converting Vital Statistics Mortality Registry Diagnosis Codes
In the Vital Statistics Mortality Registry data, "Primary Cause of Death" is coded using ICD-10 (four characters) in the variable named PRIMARYCAUSEDEATH. It is important to remember that vital statistics is coded following the WHO convention for ICD-10 not the CIHI ICD-10-CA. At the four character level they are supposed to be identical but the CIHI 2001 conversion files do not contain all of the four character codes when ICD-10-CA is coded completely to a 5 or 6 character length.
The conversion for diagnosis is not perfect for the vital statistics file. This is likely due to differences between ICD-10 and ICD-10-CA. The CIHI conversions do not appear to contain some WHO codes. This appears to happen when CIHI has added one or two characters to the WHO code and then required that ICD-10-CA to be coded to that level. This means the four digit level is not a valid ICD-10-CA code (e.g. C349 does not exist but C3490 does).
The code that is used to capture these differences is available in the SAS code link below. This is done by adding one, or two, additional 0's to the ICD-10 code. The assumption has been made that the first code (0) in the list is the most common and has actually been coded - THIS IS NOT ALWAYS THE CASE. Eventually a complete format should be made or bought that includes all of the codes. When the converted ICD-9 codes are used for mortality data it may be most appropriate to limit the data to the three or four character level in any case.
See the SAS code below for an example of converting ICD-10 to ICD-9 for Vital Stats mortality data.
When one or two '0's are added to the ICD-10 code there is generally only one ICD-9-CM code that matches the whole category.
There are a few additional codes that are not captured using the above. Where there have been modifications the grade should be noted as '3'. These modifications have been supplied in the above format and should be reviewed prior to running any new year of data. The additional codes include:
ICD-10 ICD-9-CM Notes
A16__ 011,012 Tuberculosis
B20_ 042 HIV related codes CIHI codes as B24
B21_ 042 HIV related codes CIHI codes as B24
B22_ 042 HIV related codes CIHI codes as B24
B23_ 042 HIV related codes CIHI codes as B24
D37_ 2351 Neoplasm of uncertain or unknown behavior of oral cavity and digestive organs
E148 250 Unspecified Diabetes
G82_ 3441 Paraplegic
G938 3488 Other conditions of the brain
J38_ 4783 Paralysis of vocal cords or larynx
J46_ 493 Asthma
Each conversion from ICD-10-CA/CCI to ICD-9-CM has been graded. As mentioned above, these grades represent the "goodness of fit" for the particular conversion. If you are converting files, you should create new variables for both the ICD-9-CM codes and the grade. Test the grade variable with a SAS® PROC frequency. Poor fitting observations should be checked.