SNOMED CT PaLM Mapping Best Practice

This guide describes best practice for labs to follow when mapping source terminology data representing patient test results to SNOMED CT Pathology and Laboratory Medicine (PaLM) and to other coded data elements in the Pathology FHIR Specification.

The principles outlined in this document can be applied more broadly, to help you map to terminologies and code sets used in other areas of healthcare. Therefore, the pathology and laboratory medicine terminology mapping requirement can be considered a use-case to draw out the principles of best practice for automated, user-guided terminology mapping.

The intended audience for this document includes:

• pathology lab IT managers
• pathologists/biomedical scientists involved in the clinical review of maps
• suppliers of mapping software
• stakeholders seeking transferable best practice guidance on terminology mapping

This document should be read in conjunction with:

• DAPB4101 Information Standards Notice (Amd 63/2023)
• NHS England Data Science Team - Advanced Analysis Components to Support SNOMED PaLM Mapping Project

Created by NHS England, SNOMED CT PaLM is a terminology that more accurately represents pathology and laboratory medicine patient test result codes (‘reportables’) than the legacy, outdated Read PBCL codes currently in use. Together with the Pathology FHIR Specification, SNOMED CT makes up the new DAPB4101 Information Standard that governs lab to GP reporting. It is endorsed by the Royal Colleges, the BMA, and the Institute of Biomedical Science. The implementation of SNOMED CT PaLM will bring many benefits, not least pandemic preparedness, with its ability to add new national reportables for new lab tests.

Due to the limitations of many laboratory information management systems (LIMS) SNOMED CT PaLM cannot yet be used natively by most labs, so mapping of ‘local’ reportables to SNOMED CT PaLM reportables is required.

The International Organization for Standardisation (ISO) defines mapping as:

‘the process of associating concepts from one terminological resource to concepts in another terminological resource and defining their equivalence in accordance with a documented rationale and a given purpose.’

However, whilst prevalent in digital healthcare, mapping can be laborious, can introduce error, can result in variation, and requires ongoing maintenance. 

Consequently, NHS England’s PaLM Mapping Project team have sought to establish the best and most efficient way that labs can map to SNOMED CT PaLM and to other coded data elements in the Pathology FHIR Specification; these being key data items that allow the pathology report to be represented as structured data, and how best to create and maintain assured map tables and value sets. Activity chiefly centred on formulating, testing, and evaluating a range of mapping strategies and mapping tools.

Below is an example of a local reportable to SNOMED CT PaLM concept map:

It is important to acknowledge that much of the best practice established whilst undertaking this project can be applied universally to terminology mapping. A wider view beyond the scope of supporting DAPB4101 is encouraged, as terminology mapping supports interoperability across many aspects of digital healthcare.