Informatics 2000feb6

Journal of Informatics in Primary Care 2000 (February):15-17


Towards a "New" International Terminology for Health: Read Clinical Terms and SNOMEDÒ

NHS Information Authority (Coding and Classification)
Woodgate, Loughborough, UK

SNOMED International, College of American Pathologists
Northfield, Illinois, USA

Correspondence to Dr Colin Price, NHS Information Authority, Woodgate, Loughborough

[This paper was delivered at the Annual Conference of the Primary Health Care Specialist Group of the British Computer Society, at Cambridge, England, in September 1999.]


In April 1999, an agreement was announced between the National Health Service (NHS) and the College of American Pathologists (CAP) to develop a joint terminology from the basis of SNOMED-RT1 and the Clinical Terms Version 32 (The Read Codes). Over a period of three years – until late 2001 – teams from both organisations will work on the merger of these leading terminologies. CAP will deliver a comprehensive "New Work", which builds on the strengths of both.

As the world’s largest medical society composed exclusively of pathologists, with nearly 16,000 members, the CAP has been involved in clinical terminology development since the mid-1960s. The Systematized Nomenclature of Medicine (SNOMED) is used in over forty countries worldwide. It is generally recognised as the standard for use in pathology systems throughout the world, including the UK. SNOMED-RT, the international reference terminology, is currently undergoing beta-testing in over thirty organisations. The NHS purchased the rights to the Clinical Terms (The Read Codes) in 1990, and developed Version 3 during a series of multi-professional Terms Projects from 1992–95.


Both current works incorporate most of the well-recognised desiderata for modern clinical terminologies proposed by Cimino3. Parallels between the two file structures are readily apparent, in particular, the distinction between terms and concepts; the use of meaningless identifiers; the representation of relationships (including hierarchy) in simple relational tables; and the provision of formal semantic definitions, using KRSS description logic in SNOMED-RT and Object~Attribute~Value triples in the Clinical Terms (see Figure 1). The multiple hierarchies and explicit semantic definitions enable clinicians and researchers to retrieve and aggregate data more completely and consistently.

Postoperative oesophagitis
  • Site: Oesophagus
  • Morphology: Inflammation
  • Occurrence: Postoperative
Postoperative esophagitis
  • Esophagitis NOS &
  • (assoc-topography Esophagus) &
  • (assoc-morphology Inflammation) &
  • (assoc-etiology Postoperative state)

Figure 1: OAV (Clinical Terms) on the left and KRSS (SNOMED) descriptions of Postoperative oesophagitis on the right. In many cases, transformation from one representation to the other is automatic.

Active discussions are now underway to establish an agreed structure for the New Work according to the principles outlined in Figure 2:

  • Defining boundaries
  • Using the best of both file structures
  • Reusing content
  • Facilitating implementation
  • Capitalising on existing testing/evaluation
  • Migrating existing users
  • Ensuring scalability and maintainability


Figure 2: New Work Design Principles



SNOMED has its origins in the Systematized Nomenclature of Pathology (SNOP) whereas the early Read Code versions were designed to support primary care medical practitioners. However, from these diverse origins, both terminologies now aim to provide comprehensive coverage of the health care domain. An important component of the merger process is to identify concepts that are common to both terminologies. This often requires inspection by expert authors (or comparison of semantic definitions) to ensure that the concepts are clearly identical and that there is no ambiguity of meaning. Preparatory work is already under way comparing the anatomy chapters in both CTV3 and SNOMED.

A further area of work is to match the attributes/roles used in semantic definitions in both schemes and to agree on the sets of applicable values. Referring back to Figure 1, we can see that the anatomical attribute Site in CTV3 is used to reference an anatomical structure (oesophagus); the equivalent role in SNOMED is assoc-topography. Once these matches have been agreed, and providing that the value sets (in this case the anatomy chapters) are congruent, the merger process becomes much simpler4.



A New Work Authority – a governing body of experts to oversee strategy and operations – will include representatives nominated by the CAP and the NHS. An Editorial Board with equal numbers of voting members nominated by the CAP and NHS will provide scientific guidance and allow incorporation of the knowledge and experience of clinical specialists, during both development and subsequent maintenance of the combined terminology.



The collaboration between the CAP and the NHS is a significant turning point in the development of healthcare terminologies and undoubtedly provides our best opportunity to create a global standard. Early joint working has already highlighted the commonality between the partners, not just at the "data structure" level, but also in a shared mission to provide a high quality terminology to support the delivery of patient care.



1 Spackman KA, Campbell KE, Coté RA. SNOMED RT: A Reference Terminology for Health Care. In: Masys DR (Ed.). Proceedings of the 1997 AMIA Annual Fall Symposium. Hanley & Belfus, Philadelphia, 1997:640–644
2 O'Neil MJ, Payne C, Read JD. Read Codes Version 3: A User Led Terminology. Meth Inform Med 1995; 34:187–192
3 Cimino JJ. Desiderata for Controlled Medical Vocabularies in the Twenty-First Century. Meth Inform Med 1998; 37:394–403
4 Price C, Brown PJB, Schulz EB. Comparing Primitive Concept Fields in Clinical Terminologies. In: Masys DR (Ed.). Proceedings of the 1997 AMIA Annual Fall Symposium. Hanley & Belfus, Philadelphia, 1997:985


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