Terminology Migration FAQs

Migration: Antecedent SNOMED versions and codes / products to UTL including UOM

Q. What is the relationship between UTL and SNOMED CT?

UTL is composed of results expressed using SNOMED CT elements – but has a preferred name attached to every ‘pre-coordinated’ observable entity type SNOMED concept.   

Q. Where can I find resources related to conversion and translation e.g. Read (Pathology bound code list) → SNOMED CT and SNOMED CT→ OPCS/ ICD?

Mapping tables are available on the Technology Reference data Update Distribution (TRUD) website at the following link: https://isd.digital.nhs.uk/trud3/user/guest/group/0/search/results?q=map 

QDo I Map to UTL or SNOMED CT for blood sciences? I’m confused! I Need to know as I have to estimate how long it will take

SNOMED CT is part of the UTL and coding should be using SNOMED CT -Please see notification from the Data coordination Board at the following link:  https://digital.nhs.uk/data-and-information/information-standards/information-standards-and-data-collections-including-extractions/publications-and-notifications/standards-and-collections/scci0034-snomed-ct 

Q. Laboratory input is essential  when discussing with developers, otherwise you develop what you want, not what the laboratory needs. What Level of input have laboratories had so far?

The UTL was developed based upon the tests used in Exemplar trust labs, users have been consulted via the Professional Record Standards Body but need to be consulted further and this is intended to be undertaken with the First of Type Implementation sites. If you are interested in being a First of Type site, please contact pathologyanddiagnostics@nhs.net  

Q. Where can I find Tools for the Migration from Antecedent SNOMED versions to SNOMED CT?

The migration toolkit is available for use from the TRUD website, link: https://isd.digital.nhs.uk/trud3/user/authenticated/group/0/pack/8/subpack/266/releases.

Please download from TRUD the SNOMED Legacy Data Migration Sub-pack and read the documentation.

Any further questions please contact information.standards@nhs.net 

Q. For systems currently using an antecedent version, is the expectation to change the Laboratory Information Management Systems (LIMS) interfaces to use SNOMED CT codes, or allow users to carry on and just manage the output?

The expectation for the LIMS interfaces is to handle native SNOMED CT the antecedent versions are for legacy data compatibility and for making migration easier. 

Q. For planning /business case need I would appreciate cost/time estimates of migration and schema for validation

Migration costs would depend on the individual suppliers, the proposal is that subsequent procurement tenders should have SNOMED CT compatibility as a mandatory requirement. Please see link to notification from the Data coordination Board  https://digital.nhs.uk/data-and-information/information-standards/information-standards-and-data-collections-including-extractions/publications-and-notifications/standards-and-collections/scci0034-snomed-ct


Q. My LIMS provider has advised that the system will support SNOMED CT for Histology but I would like to know if we should also be changing from read codes to SNOMED CT for all of the other departments e.g. Biochemistry, Haematology, Microbiology etc. what advice can you give me if our current LIMS provider cannot support SNOMED CT for these departments?


SNOMED CT is a NHS approved fundamental standard (SCCI0034); including implementation guidance which states all providers of health related services where the flow of information for the direct management of patient care comes into the NHS must use this standard by 1 April 2020. SNOMED CT can be used in all areas of Pathology, including laboratory science and other diagnostics.

In June 2019, NHS England and NHS Improvement’s National Pathology Optimisation and Delivery board identified IT requirements for establishing and implementing the 29 Pathology Networks across England including the minimum set of standards to ensure interoperability as end to end systems are deployed. 

They wrote to all Trust CEO’s and Financial Directors to provide guidance stating “it is therefore mandatory that all systems purchased and deployed into the NHS going forward meet the following standards for requesting, reporting and communicating diagnostic test results: 

1) SNOMED CT (Systematized Nomenclature of Medicine -- Clinical Terms)  

2) FHIR (Fast Healthcare Interoperability Resources) message standard.  

3) Open access of systems - No restrictions on connections and interfacing between clinical systems” 


Information about the Work NHS Digital’s Pathology business product team is currently undertaking to support this transition can be found at the following link:


If you would like to know more about our work or become more involved, Please contact us at Pathologyanddiagnostics@nhs.net




Units of Measure

Q. Given a test in the UTL, what is the preferred UOM?

Almost all (~98%) tests in the Initial draft release of UTL covering approx 350 tests have a proposed “preferred UoM” assigned. We would expect to maintain this approach to future expanded releases of UTL.

Q. Given sample type and method, what is the UOM?

The UTL has a preferred sample type where these are significantly different i.e between plasma and serum. For those that are not clinically significant it states plasma or serum.

A property type (e.g. mass, molar or activity concentration) is assigned, and a proposal for the preferred Unit of Measure (e.g. mmol/L or nmol/mL).

The UTL has separate codes where methodology is clinically significant e.g. enzymatic or colourimetric. These are still under review for immunometric assays which are known to have variation in results for the same method type and unit of measure and are in consultation with clinical experts on the number of codes required

Q. What’s the difference between Mass concentration and Molar substance concentration in your observables?

Mass concentration relates to g/l or mg/L and Molar concentration relates to mmol/L or pmol/L. The coding allows analytes to be reported in different units, but be coded separately to ensure they are not misinterpreted.

Q. In the Interim Units guide (IUG) report (Units of Measure in Pathology Reporting) the caret character (^) used to represent exponentiation (e.g. 10^6 for "millions") is replaced by 10*6 (which I read as 10 x 6= 60). HL7 can handle either, why choose the asterisk (*)?

 For anyone with a software background this usage is jarring and likely to confuse. Governance to make these decisions on behalf of the NHS is on the Product backlog and once in place will manage this and make sure the potential impacts on labs and suppliers etc. are considered, and patient safety is not compromised 


Message specification

Q. Do I have to wait for my order comms to be ready for FHIR? 

Yes, please speak to you system supplier re their roadmap. 

Q. What is your intention regarding Pathology reference ranges?

Pathology harmonisation is a difficult to agree area, some tests have accepted and harmonised ranges, but most don't.

NB: the ability to exchange reference ranges are incorporated in the Pathology FHIR message specification

 Q. Why are we  focusing solely on FHIR, as FHIR is not a prerequisite for Interoperability?

The Generic Information Model means it doesn’t necessarily have to be FHIR however FHIR is the direction of travel. Information Standards are going to be based on SNOMED and FHIR.

SNOMED and relationships to other NHS Digital Products

Q. Will we be able to create our own Local Refsets (subsets)?

The SNOMED CT ontology allow creation of reference sets, however it is likely that the updates related to the refsets should be checked and maintained by the creators, using the yearly releases of the SNOMED CT international or UK release.

Q. Are there plans for a small Implementation group for HOW we move from old to new? 

In the short term a subgroup of the PINUG (which is clinically not NHS Digital led) could establish itself or could be combined with a wider SNOMED implementation group – this is on NHS Digital’s wider backlog but is dependent upon agreed priorities and funding for it to be centrally led.

Q. Are you putting method of analysis in SNOMED CT? e.g. you shouldn’t graph creatine from 2 different methods.

Yes – this should be handled from within SNOMED CT

Q. What is the priority for lab disciplines? As LIMS providers, we have to prioritise any developments to maximize the benefit to as many customers as possible.

The Current priority is blood sciences (biochemistry and haematology) as these made up the majority of the commonly requested tests. Microbiology is being reviewed for the next phase. Priorities for the other disciplines hasn’t been confirmed at this stage. 

Q. For reporting from Lab to GP system, surely the GP System has to be ready to receive the messages. Are TPP and EMIS on board?

Yes, All the major Primary Care suppliers are already SNOMED CT Compliant and have plans to utilise the Pathology FHIR message specification.

Q. If only using mapping in BHI, at what level is SNOMED CT applied? At test creation? Result entry? at reporting?

SNOMED should be used when exchanging clinical data between care settings – please see DCB notification for further information https://digital.nhs.uk/data-and-information/information-standards/information-standards-and-data-collections-including-extractions/publications-and-notifications/standards-and-collections/scci0034-snomed-ct

Q. Is there any recommendation to Integrate browsers into LIMS interfaces? If so, is there any ongoing cost to the LIMS provider and /or customers?

This is a choice for the trusts and the systems that they purchase

Q. I still don’t know what the expectation is from LIMS providers. Each time the focus/message is different. Is mapping enough? If mapping is enough, why all the talk about API’s? 

This approach is not about mapping the existing list – mapping is only an intermediate step, mainly for legacy data. The new code list/set needs to replace the existing list, but the model is not implementable by simply replacing one list with another – there is a fundamental change in the data model of the request-test-result cycle.

Please see link below to the secretary of state's vision for health re building a data layer with registers and APIs for further information.


Q. I would like to know about Post coordination requirements in terms of implementation: storage and retrieval. A further suggestion: some tool to help on mapping local codes such as RELMA provided by LOINC. I presume most sites are using local codes and definitions, except for primary care messaging

Local mapping is not a good idea from a standardisation perspective, only acceptable to access legacy data. The roadmap is to replace the old list-based model with a new data and flow model.

Please see the  SNOMED International mapping tables from LOINC at the following link https://www.snomed.org/news-and-events/articles/loinc-snomed-ct-cooperation-project-technology

Q. Are ODS codes available  to Non-consultants + non-GP’s?

Yes, ODS codes are available to view at the following link https://digital.nhs.uk/services/organisation-data-service