What is HL7?

Health Level Seven (HL7) is a messaging standard that created in the late 1980's by hospitals and vendors interested in creating an common standard for exchanging health information. The context was health but more specifically hospitals.

HL7 comes in two main flavors Version 2 and Version 3. These versions have entirely different formats and are different development tracks. Standards work is still be done on both versions. Most legacy HL7 systems support Version 2 while many newer non-Hospital systems are beginning to to support Version 3. Systems that speak one version normally do not speak the other version.

The CDC has asked immunization registries to support HL7 Version 2 messages that pertain to immunizations. Standardization work is being done for immunizations for Version 3 but none of this is yet recommended by the CDC. Many immunization registries are still working on their HL7 Version 2 support and are unlikely to support Version 3 any time soon.

Here is a sample HL7 Version 2 message:

MSH|^\&|||||20080320102346||VXU^V04|20080320102346.693458||2.3
PID|1||505^^^^MR||MOUSE^MICKEY^^^^L|19281128|M|
RXA|0||20080319|20080319|90715|

This is very basic but shows a patient by the name of "MICKEY MOUSE", born "11/28/1929", who received a vaccination with CPT code '90715' on '03/19/2008'.