The LOINC® groups project by the Regenstrief Institute aims to give you a flexible, extensible, and
computable mechanism for rolling up groups of LOINC codes for various purposes.  
Starting in 2017 with support by the National Center for Advancing Translational Sciences, LOINC groups organize collections of codes as defined by LOINC’s six-axis terminology model.
For example, rather than searching for individual variations of ‘blood glucose measurements’, LOINC groups can bundle blood glucose measurement codes under a single source.

LOINC groups are structured by their defined axis values. This is done by creating high-level Parent Groups which are used as templates for sub-groups and the codes contained within each sub-group.
Let’s look at the structure of a LOINC Parent Group as an example: 

Parent Groups contain broad ranges of codes due to fewer axis constraints. Sub-groups are more granular, further specifying axis value requirements for codes under the Parent Group template. This allows sub-groups to constrain codes according to a specific use case. To see how Parent Groups correspond to a list of sub-group LOINC codes, we need to create a sub-group that constrains the list of aggregated Parent Group codes. Let’s take a look at LOINC group LG7967-5 Glucose|MCnc|PT|ANYBldSerPl as an example:

By specifying the required sub-group axis values, the list of codes should contain ‘like’ terms with similar definitional meaning or use. The following list is an example of the codes contained within LOINC sub-group LG7967-5 Glucose|MCnc|PT|ANYBldSerPl.

As more use cases are identified, LOINC groups aim to enable users with understandable, reproducible, and useful collections of codes that better group similar content. Currently, the Regenstrief Institute is asking the community to assemble and submit LOINC groups through the LOINC Groups Submissions page. Submitted groups will be reviewed by the community and potentially nominated for inclusion in future LOINC® releases.