The OBX segment is a jerk - how to use encapsulated data in an OBX segment

So say your hospital has this application that makes patient results (like the results after a procedure), and it does it in a PDF with embeded pictures and a nice layout and it looks all awesome. You want to get this PDF and jam it into your results repository so that the clinical staff can go to this single place to view results from different applications (if they have to log into multiple places they will get a severe case of the frowny faces). Now, it also turns out that your hospital has an 'enterprise messaging system' because that is the kind of insanity we like to get involved with in the health sector so that means you're using HL7 messages to pass information between applications.

Enter the OBR message. Ta da.

The OBR HL7 messages are used to send results, and the OBX segment of the message is what contains the actual results details.  Often they might just be holding that information as text, but you can also cram whole files into the OBX segment. The problem with the OBX is that it is a bit of a jerk and likes to be all mysterious and poorly documented by systems that both produce and consume OBR messages.

The second field in the OBX determines how you are sending your data. You've got options here; these seem to be the least useless options of putting data into an OBX:

RP = Reference pointer
ST = String
FT = Formatted text
TX = Text data
ED = Encapsulated data

The string, text and formatted text are sending the results as string data.  The reference pointer allows you send a link to a file (e.g. on a network drive).  Encapsulated data allows you to embed the entire contents of a file (e.g. a PDF or a DOCX) into the message.

A message with two sets of results (two OBX segments) where one is formatted text and one is encapsulated data looks like this:

MSH|[snip]
PID|[snip]
PV1|[snip]
ORC|[snip]
OBR|[snip]
OBX|0001|FT|1006^MCH^L^28539-5^^LN||"this is formatted text"|pg|||||I
OBX|0002|ED|1003^Haemoglobin^L^718-7^^LN||ClientFile^application^pdf^Base64^CBSL0xlbmd0aCA2Ny9QcmV2IDk0MjIvUm9vdCAxMSAwIFIvU2l6ZSAzMi9[snip]

So, the OBX which is set to encapsulated data ('ED') has the base64 encoded binary contents of a PDF jamed into the OBX.5 field.  That's kind of cool!

What these message actually look like on the recieving system I guess depends on how the application deals with them.  In our results repository (Eclair), if you send a single ED OBX (containing for example a PDF) it will open and display the document in panel as shown to the left.









If you send multiple OBX segments then the ED ones will show with clickable icons.













Yuuussssss.