HL7 v2 is the veteran healthcare messaging standard, born in the 1980s, that still carries the bulk of event traffic inside hospitals. Messages are pipe-delimited text — fields separated by | characters in a defined segment structure — and the common message types map to real clinical events: ADT for admit, discharge, and transfer; SIU for scheduling; and ORM and ORU for orders and results. When a patient is admitted or a lab result is finalized, an HL7 v2 message is typically what announces it to the rest of the hospital's systems in near real time.
The standard is famously loose. The specification leaves much optional and locally negotiable, so almost every site customizes its interfaces — hence the running joke that if you have seen one HL7 v2 interface, you have seen exactly one. This is the opposite of the predictable, web-friendly REST world of FHIR, and it is why integration effort is hard to estimate from the standard alone.
For a telemedicine platform, HL7 v2 is what you meet when real-time event flow matters more than REST convenience — for example, learning the moment a patient is checked in so a virtual visit can begin, or pushing a result back into the hospital. The practical implication is that each interface is a bespoke negotiation with that hospital's integration team, usually mediated by an interface engine, and you should budget for per-site mapping and testing. The common mistake is assuming one HL7 v2 implementation will port cleanly to the next hospital; in practice the segment usage and custom fields differ every time.
