Use of attachments

Use of attachments, either in test orders or referenced in diagnostic reports is still under discussion.

There are a number of elements, such as PDF test reports and RoD documents which the national strategy indicates should not be stored on a national service, but instead should be accessible directly from the originating/data controller system. For the alpha and beta phase, where suppliers would struggle to meet timescales, the documents will be stored in the national service to simplify integration, but with a clear roadmap for changing where the documents and data are stored and retrieved. This could use a service such as NRL, possibly proxied through the national service to remove the risk of consumers losing access to the data and to decouple the development and migration of providers from a central document store to distributed document storage and retrieval.

This section will be updated as requirements are elicited.

Examples of attachments which may be used are:

• PDF copies of patient history and diagnostic reports
• DICOM or other images included as part of the patient history
• Variants of Unknown Significance (VUS) files which may be attached to genomic reports

It is expected PDFs in messages will be sent within the body of the FHIR message as a base64 encoded string.

Images and VUS files may be quite large in size so a separate image/variant store may need to be used to host this data centrally. Alternatively, suppliers can ensure this data can be queried and retrieved by the Genomic Medicine Service, either via NRL or externally queryable APIs, allowing these attachments to be referenced by their URL as per Bundle referencing.

Considerations

There is no preference from FHIR on use of either embedded documents vs. links within the presentedForm element, though there are potential concerns on either side, e.g. a search on DiagnosticReport, when using embedded links, could result in responses exceeding allowed sizes thereby necessitating the need to strip the data on search, but include this data on targeted reads. On the other hand, if links are used, these may expire or no longer resolve, especially where the service is relying on third party hosting, e.g. provided by labs, to expose the files. Users would also potentially run into issues due to firewalls having to be configured for each endpoint or source systems having to either expose data through internet facing links (an IG issue) or host data behind HSCN, increasing burden on querying systems to retrieve the data.

In production, a central document repository would address both issues, where users register the document on a National Document Repository (NDR), provided by NHS England, and use the link to the NDR resource within the the Genomic Order Management Service. As no such service currently exists, the preference in Alpha is to embed the PDF within the DiagnosticReport sent to the Genomic Order Management Service.