Many countries have developed medical terminology codes and descriptions based on their own individual needs. These may be derived from another countries’ data, current or past, or be totally unique and created “from scratch”. When there is a requirement to integrate or compare data encoded to different countries’ code sets, a crosswalk (mapping) between the different terminologies is needed so one is not comparing apples to oranges. Because the code sets can be very different in terms of terminology models (structure/design/organization), granularity (details/definitions), comprehensiveness (inclusions/exclusions), usage and other factors, mapping between a pair of country-specific terminologies can be challenging. The following tips may help:

•Determine if the mapping needs to be exact matches (same or clinically equivalent) or can be  “fuzzy” (best fit, broader than, narrower than, etc.).
•Check if the mapping must be one to one (i.e., one code from the source terminology must map  to one and only one code in the target terminology) or can be one to zero (no match) or one to  many (possible matches).
•Note that the mapping is unidirectional, i.e., from the source (first) terminology to the  target (second terminology); the reverse (mapping from the second to the first) is not  automatically equivalent. This is especially true if the mapping is not exact and one-to-one.
•Realize that mapping should be use case specific – the purpose (intended usage) of the mapping  can influence the decision points above.

As a case study, we evaluated mapping between the Canadian Classification of Health Interventions (CCI) and the US procedural coding system, ICD-10-PCS. The CCI data includes all types of healthcare interventions, including physician, nursing, ancillary and facility services. ICD-10-PCS is used to collect data, determine payment, and support the electronic health record for all inpatient procedures performed in America. Examples of challenges encountered in mapping CCI codes to ICD-10-PCS are:

•Different meaning of terminology: for example, Extraction in CCI taking out, without excising, all or part of the solid content of a body site is mapped to Extirpation <of a body site> in PCS.
•Different handling of procedural approach: for example, CCI assigns every procedure a specific type of approach, for instance, percutaneous, percutaneous/needle, endoscopic, open, combined endoscopic/abdominal approach. PCS codes are   specific to a single approach. In circumstances where a procedure    starts out endoscopic and ends in an open approach, only the open approach is listed. Laparoscopic-assisted procedures still considered an open approach.
•Different terms used for the same procedural approach: for example, CCI has many codes for procedures performed on the cornea with open approach. PCS approach options for the same procedures are percutaneous or external but not open.
•Excision and Resection can be confused in PCS mapping. Excision is removal of some of a body part whereas Resection is removal of all of a body part. There are exceptions for bone marrow and endometrial biopsies which are considered.    Extractions in PCS with the additional qualifier of Diagnostic.
•CCI included many codes and descriptions for various body positions during labor and delivery. These types of procedures are not included in PCS.

If you have questions regarding mapping between different terminologies or would like our help, please contact us.