Project Details Piloting NPU-SNOMED CT mapping

Project No.: 
Start Date: 
01 July 2014
End Date: 


Both IFCC, IUPAC and IHTSDO, owner of SNOMED CT, strive for harmonization between healthcare terminologies to avoid unnecessary redundancy and duplication of work. To achieve this, collaboration between terminology development organizations is needed. In practice, this collaboration means agreement of principles as well as specific meaning of terms.

In 2009, a feasibility study was performed with C-NPU, IHTSDO and Regenstrief Institute as participating organizations. In the study, some 200 CNPU terms were mapped to SNOMED CT. The study showed that harmonization between terminology developers is achievable. The next step, described in this project, is to investigate how NPU – SNOMED CT harmonization can be realized practically and how a method aiming to meet set quality criteria can be developed and applied.


Three distinct activities needs to be addressed by the project:

  1. The elements of which NPU terms are constructed needs to be mapped to SNOMED CT substances, body structures etc.
  2. Existing NPU terms (dedicated kinds-of-property) will be mapped through identification of mapping patterns. E.g. all CNPU concentration terms could be mapped in the same way. The development of such patterns is important for consistency.
  3. The ongoing maintenance and addition of new content to the NPU – SNOMED CT map.

Items 1 and 2 are sub-projects while item 3 is a continuous process.

This project will support the establishment of this process.

In this pilot project a subset of NPU content will be mapped:

  1. 400 NPU elements (5 % of the total number of elements) and
  2. 400 NPU terms (2 % of the total number of CNPU terms)

The subset will be selected to be representative of CNPU content that is used in production systems. The project, being a pilot project, will deliver guidance for a future larger scale project. This guidance will specifically include identification of a mapping workflow and the quality assurance of mapping results.


This project builds on the outcome of the earlier work performed under projects 2006-008-1-700 and 2009-005-1-700.

May 2017 update – The project has aimed to explore possibilities of large scale mapping between the NPU terminology and SNOMED CT. A selection of 863 unique NPU codes in use in Denmark, Norway, and Sweden were chosen for the pilot. The NPU codes had 598 distinct system, system specification, component, and kind-of-property elements of which 376 (63 %) could be assigned a SNOMED CT code. Large groups of non-matching elements were antibodies (n=99) and genes (n=20) which are both represented slightly differently in SNOMED CT. The 376 mapped elements can be used to represent approximately 500-600 of the 863 NPU codes.

Oct 2020 update – A Technical Report ‘PROPERTIES AND UNITS IN THE CLINICAL LABORATORY SCIENCES – PART XXVI Piloting NPU-SNOMED CT Mapping’ co-authored by Daniel Karlsson, Helle M. Johannessen, Ulla M. Petersen, Urban Forusm, and Gunnar Nordin, is under final review.

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Page last updated 19 Oct 2020