Artifact name change

With the release of LOINC version 2.73 in August 2022, the Multiaxial Hierarchy artifact has been renamed Component Hierarchy by System. This change is to align the hierarchy name among others available in LOINC. The following indicates how the name is now reflected within the LOINC Complete download. Aside from file name changes, there is no difference in the structure of the artifact.


├── MultiAxialHierarchy
│   ├── MultiAxialHierarchy.csv
│   └── MultiAxialHierarchyReadMe.txt


├── ComponentHierarchyBySystem
│   ├── ComponentHierarchyBySystem.csv
│   └── ComponentHierarchyBySystemReadMe.txt

The LOINC Component Hierarchy by System is a computer-generated organization of all LOINC codes

The Component Hierarchy by System (CHBS) organizes LOINC codes based on multiple axes of each term. LOINC Parts comprise all of the branches in the CHBS, and LOINC terms comprise all of the leaf nodes. The CHBS is generated using an automated process based on the separate Component hierarchy, which is maintained by hand, as well as the System and Class for each term. These hierarchies are not meant to be pure ontologies, and rather are tools for organizing sets of codes within different domains.

In the Hierarchy Browser web app, the CHBS can be used to view and visualize LOINC terms.

LOINC Hierarchy Browser

The CHBS was originally created for the Laboratory domain, and over time, specific clinical domains (e.g., Radiology, Document Ontology) were added. The CHBS released with LOINC Version 2.61 was a major update that incorporated all LOINC terms (across all domains), and going forward we plan to continue including all LOINC terms in the hierarchy.

The CHBS contains four top-level branches to match the four broad types of LOINC codes: Laboratory, Clinical, Attachments, and Survey. All of the domains other than Radiology (which is contained within the Clinical branch) are organized by Class, Component, and finally the System. Radiology terms are organized by System (Region imaged and/or Imaging focus) followed by the Method (Modality).

Each top-level branch (except for Attachments) contains a "NotYetCategorized" node, which includes all terms in a given Class that could not be placed elsewhere in the hierarchy based on an issue with Component placement in the Component tree. Note that none of the Survey Components are included in the Component hierarchy, so all of the Survey terms are in the "SurveyNotYetCategorized" node. Over time, we intend to more fully develop the hierarchies in these areas and reduce the number of LOINC terms in "NotYetCategorized" branches.

File Contents

A description of this artifact's primary file, ComponentHierarchyBySystem.csv, follows below.


LOINC Complete

Your LOINC login is required to download. This accessory file is available within the combined LOINC file. Get more information on files included within this zip archive.

Version 2.76
Released 2023-09-18
Size 68.97 MB

API Access

The hierarchy of all LOINC terms cannot be retrieved from the LOINC API using HL7 FHIR at this time. We are working to make the parent and child(ren) relationships for each Part and the parent Part for each LOINC term available through the FHIR API.

See our documentation for more information on how to use the Terminology Server including example requests.

File Description


This file contains all LOINC terms and uses the following columns to represent them in a hierarchy.

Column Name Description
PATH_TO_ROOT The series of Part numbers delimited by dots (.) that represent the path from the root of the hierarchy to an individual LOINC Part or term.
SEQUENCE The order in which the LOINC Part or term specified in the CODE column appears under its immediate parent (i.e., the Part in the IMMEDIATE_PARENT column).
IMMEDIATE_PARENT The parent LOINC Part that immediately precedes a given code in the hierarchy. Note that the value contained in this field is always a LOINC Part number and can never be a LOINC term number.
CODE The LOINC Part or LOINC term whose hierarchy path is being described in a given row.
CODE_TEXT The name of the LOINC Part or the Short Name of the LOINC term specified in the CODE column.