Hl7 has two forms of formatting data. Piped messages and Xml. The Xml format is easier to understand for us humans. The piped message is a bit harder to understand. The format is a bit older, based on plain text. Let’s have a look at it. I will not explain every field in the standard (hey, what are standards for!), but just look at the message structure and how to read it. I’m using this example message to explain the message structure (the message is part of the ORU_R01 .Net example):

MSH|^~\&|Otogram||||||ORU^R01^ORU_R01|||2.4^^||||| USA|ASCII
PID|1||||Family^Given^Middle^^^^L|||||||||||||
OBR|1|9999^^^||28615-3^Audiology study^LN||||||||||||
OBX|1|ED|28615-3^Audiology study^LN|1|Acrobat^text^pdf^Base64^JVBERi0xLjMKJeT jz9IKNSAwI

Every message starts with a segment describing the message header (the MSH segment). A segment always starts with the segment name, following the separation character, which separates the fields of a segment as described by the HL7 standard. Segments are always separated by a newline character.

The second field of the header is a special one. It will almost always look like this ‘|^~\&’. This strange set of characters describes the format of the message: it defines which characters are used as special characters. For example: the first character ‘^’ is used as a separator between fields in a datatype. If we would change is to a ‘#’, the message would look like this:

MSH|#~\&|Otogram||||||ORU#R01#ORU_R01|||2.4##||||| USA|ASCII
PID|1||||Family#Given#Middle####L|||||||||||||
OBR|1|9999###||28615-3#Audiology study#LN||||||||||||
OBX|1|ED|28615-3#Audiology study#LN|1|Acrobat#text#pdf#Base64#JVBERi0xLjMKJeT jz9IKNSAwI

This build in flexibility is meant to overcome compatibility issues between encoding standards.

In this case the ‘|’ is used for segment separation and the ‘#’ is used for field seperations (sometimes called components) in data types. The ‘~’ is used for repetitions (fields that occur more than once). The ‘\’ is used to signify an escape character and the ‘&’ character is used as a subcomponent separation character.

Sometimes you’ll see multiple separation characters next to each other: ‘|||’. Data between these characters is sometimes optional. If it is optional, there’s no need to show the separation characters of the subfields, it’s enough to only show the ‘|’ separator.

I hope this helps in understanding the piped messages. If you have any questions: let me know!