What is a 'message'?
In health informatics, the term 'message' is used in a fairly specific way to mean a packet of information sent between two applications, containing predefined content. Historically messages have been defined by HL7, EDIFACT and other standards organisations. Each message definition specifies the structure and contents for a particular transmission. Historically messages have been used for pharmacy orders, lab orders and results among other things. Messages have always been manually defined by groups of people within standards organisations. Semantically, they carry requests, replies, many of which are 'changes in state'. For example, an HL7v2 message is defined containing a blood film result in such a way that the complete result can be sent, or just one or two analytes, marked as corrections with respect to a previous message carrying the complete result. The same scheme is used for microbiology results, due to the culturing time and the need to generate intermediate results.
Messages have historically been developed on the assumption that the internal information models of participating applications or systems do not matter, and cannot in general be known. Systems developers have had to generate messages via a transform of their own data into the prescribed message formats.
In summary, the usual meaning of 'message' and 'messaging' in health informatics has been:
- manually defined
- fine-grained
- relatively fixed content
- supports updates and corrections
- supports stateful communication
- point to point
What is an EHR?
A generally accepted definition of an Electronic health record is a record of care that is:
- longitudinal
- patient-centric
- may be lifelong
The important thing about an EHR is that it is an accumulation of information about a patient that tells the current state of the care process of the patient as well as a history of events. Further aspects of a workable EHR include:
- versioning
- indelibility
- audit trailing of modifications and possibly reads
- privacy
Can messages be used to build an EHR?
A common idea among some practitioners in the health informatics field is that an EHR can be constructed as a series of accumulated messages. However, an inspection of what is needed in an EHR and what messages provide show that this is not the case. The following sections explain why.