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Explore and Make use of Nationally Defined Messaging APIs


Use of Attachments

Use of Attachments in Transfer of Care Documents


The Transfer of Care documents allow for attachments to be included within a structured FHIR document.

Use Cases

Senders MAY include attachments within the Transfer of Care documents. For example to include copies of related documents such as patient Advance Statements.

Format of Attachments

Senders SHOULD send attachments as a PDF. This is the default attachment support format. However, senders can reasonably expect GP IT suppliers to provide support for at least the following extensions in the table below:-

Mime Type Extension
application/pdf pdf
application/msword doc
application/vnd.openxmlformats-officedocument.wordprocessingml.document docx
application/rtf rtf
text/html html
text/plain txt
text/xml xml
image/jpeg or image/jpg jpg
image/png png
image/tiff tiff

If attachments with extensions other than the above are needed, then this would need to be agreed locally and then raised with NHS Digital for consultation with GP IT suppliers.

Attachments can only be expected to be converted if correctly referenced in the message. If an attachment is delivered to a receiving system that does not support it, a negative ITK3 response code (20005) will be returned to the sender.

When using attachments, senders are expected to conduct due diligence with regards to avoidance of macro use and insertion of URLs that direct to external locations. Appropriate anti-malware measures are expected to be taken by both senders and receivers when using attachments.

Attachment Sizes

When using attachments, message initiators are advised to restrict their overall message size to a maximum of 5MB. This initial limit has been imposed to reduce the likelihood of any GP Foundation IT supplier having to manually intervene to stop processing delays or blocks in task execution because of excessive message file sizes. This limit will be reviewed as GP Practice infrastructure improves, and demand for multimedia files increase.

Receivers of Attachments

Receivers SHOULD process attachments in-line with the rules stated in the ITK3 Messaging Distribution Specification.

Binary Resource

All attachments are carried in the FHIR Binary Resource and MUST be Base64 encoded. The FHIR Binary Resource is profiled as ITK-Attachment-Binary-1 .

Example Attachment

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