1.5 Diagnosis codes
The hospital migrated from ICD-9 (ICD, 9th revision)
to ICD-10 for recording diagnoses during the three-year period for which
data were available in this study. Under the OMOP-CDM, both ICD versions
could be mapped to the same standard concept ID in the “Condition
Occurrence” table. For example, the ICD-9 and ICD-10 codes for “Type 2
Diabetes Mellitus without complications” are “250.02” and “E11.9”,
respectively. The corresponding source concept IDs are “44836915” and
“45561952”, respectively. Both of these map to the same OMOP standard
concept ID “201826”.
Some data cleaning steps were required during the ETL process for
diagnosis codes. For example, in the source database, the diagnosis code
“I.255 Ischaemic cardiomyopathy” had the decimal place shifted by two
places and should have been the ICD-10 code “I25.5”. Since both the
code and text were in the source database, the proper mapping was
rectified by moving the decimal two places to the right and confirming
that the text with the corrected code matched the OMOP descriptor. Codes
that had more granularity than present in the OMOP vocabulary were
mapped to the parent code, such as “E14.69 Unspecified diabetes
mellitus” which was mapped to the concept ID corresponding to the
parent code of “E14.6. Unspecified diabetes mellitus” in ICD-10.