Regenstrief InstituteSNOMED International

LOINC Ontology Release Notes

Version 1.0, March 2025

This release is compliant with the SNOMED CT RF2 specification, and contains a complete set of full and snapshot release files. The production content is released in the 11010000107 |LOINC Extension module|, aligned with the 2025-01-01 version of the International release of SNOMED CT, and Version 2.80 of LOINC, released February 2025.

This release contains approximately 35,000 SNOMED CT concepts representing both active and discouraged laboratory LOINC Terms. The majority of the LOINC concepts (~76%) included are fully defined. In terms of coverage of the most used LOINC concepts, this release of the LOINC Ontology features:

  • 86 of the top 88 most used
  • 1501 of the top 2000 most used, and
  • 12,699 of the top 20,000 most used LOINC concepts.

Areas of content specifically excluded from this release include:

  • Panels where the panel members are not also included in the release
  • Veterinary specific LOINC Terms
  • LOINC Terms that have a status of “Trial” and “Deprecated”
  • All other domains of LOINC including clinical, documents, surveys, etc.

The ‘SNOMED CT Implementation Guide for the LOINC Ontology’ (http://snomed.org/loinc) contains information about development of the ontology and its implementation in systems.

Known issues in this extension release

Content Issues

  • Phrases that are not compliant with rules for proper descriptions in SNOMED CT, e.g., “non-prob.amp.tar”.
  • LOINC Terms defined by LOINC Part “Antibiotic XXX” (‘other antibiotic’).
  • LOINC Terms modeled as process observables where the Component value is mapped to a SNOMED CT calculation, e.g., 104805-7|Creatinine renal clearance predicted.
  • Terms defined by property distribution width, e.g., 30385-9|Erythrocyte [DistWidth] in Red Blood Cells is rendered as Distribution width of erythrocyte specimen at point in time (observable entity).
  • Some FSNs contain inconsistencies based on the terming of the SNOMED CT attribute value concepts.

Some terms that were removed from the final LOINC 2.80 Release for further review, were inadvertently included in the LOINC Ontology v1 release. These terms will be included in the LOINC 2.81 release, but be aware they are being reviewed further and could be released as deprecated.

  • 106017-7
  • 106030-0
  • 106035-9
  • 106036-7
  • 106037-5
  • 106038-3
  • 106039-1
  • 106041-7
  • 106634-9

Validation Issues

The following validation issues have been identified in the version 1.0 of the LOINC Ontology. While these are valid problems according to SNOMED International validation tools, they were not felt likely to be a material issue for implementors, or represent a risk of negative impact in a medical setting.

Invalid Characters (hash symbols)

Two descriptions were flagged up for use of a hash symbol (#), which is contrary to SNOMED International Editorial Policy:

Code SCTID FSN
53273-9 590721010000104 Urinalysis type of non-squamous epithelial cells panel [#/volume] – Urine by Computer assisted method (observable entity)
53276-2 590731010000101 Urinalysis type of non-squamous epithelial cells panel [#/area] – Urine by Computer assisted method (observable entity)

The LOINC Long Common Name is used directly as the FSN for panels, and is therefore not subject to SNOMED Editorial policy.

Descriptions exceeding 255 characters.

Fully specified names (FSNs) in the LOINC Ontology are determined programmatically by assigning attribute values to slots in a template. Because of this, LOINC concepts that use individual parts with long names can combine to form an FSN with more than the current limit of 255 characters. SNOMED International has given notice that it intends to extend this limit, and so systems designed to work with the LOINC Ontology (and SNOMED CT in general), are encouraged not to “hard code” field size limits for descriptions.

Validation reported that 3 descriptions (two of which belong to the same concept) have exceeded 255 characters:

Code SCTID FSN
48643-1 562611010000103 Volume rate per area of glomerular filtration rate in point in time in plasma or serum or whole blood by modification of diet in renal disease creatinine calculation formula relative to 1.73 square meters body surface area and adjusted for African race (observable entity)
48642-3 562601010000101 Volume rate per area of glomerular filtration rate in point in time in plasma or serum or whole blood by modification of diet in renal disease creatinine calculation formula relative to 1.73 square meters body surface area and adjusted for non-African race (observable entity)

Non-compliance to Machine Readable Concept Model (MRCM) specifications

Since the LOINC Extension is produced using a, template based transformation of officially published LOINC concepts, the LOINC Ontology team (representing both SNOMED International and Regenstrief Institute) are not concerned that modeling will be introduced that will ultimately contravene the SNOMED International Machine Readable Concept Model (MRCM). A number of modeling questions have been raised through this collaboration, and each time this has resulted in an expansion of the MRCM to allow for a wider range of expression. We have not yet experienced any situation where an MRCM restriction has been found to indicate a content problem, or require a change to the LOINC Ontology.

With the 1.0 LOINC Ontology being based on the January 2025 SNOMED International edition, changes made to the MRCM more recently (e.g., in February) will not become available to the LOINC Ontology until our next release. In the meantime, MRCM validation checks will report a small number of model contraventions – particularly in the area of cardinality (i.e., rules about how many of each attribute can appear in a concept), which we expect to have resolved by the time the next release is published.

General comments about case significance

In general, LOINC is less prescriptive about case significance than SNOMED CT. SNOMED CT has a policy of capitalizing descriptions, and providing a separate indicator to say if this capital can safely be made lower case. There are concepts in LOINC where descriptions start – very deliberately – with a lower case character, when Tall man lettering is being used. For example in 614921010000103 |fentaNYL and Norfentanyl panel - Serum or Plasma (observable entity)|