2025-07-22 - Laboratory Terminology Standards WG Meeting

Inheres_in 

ratios, fractions, mass content

Daniel - not in our Top 100 list, but we do have body structures though, as cell structures (leukocytes etc.) are body structures. We would I guess only use a specimen value of inheres in if the observable was specifically about the specimen (e.g. specimen volume).

I would assume that the first one would inhere in the liver, for the second one there is both 395508003 |Hair - material (substance)| and 386045008 |Hair structure (body structure)| to consider. 119326000 |Hair specimen (specimen)| is defined by the body structure.

A (patient) system is an “arbitrarily defined part of the universe” and the domain of “Inheres in” is any material entity (substance, organism, body structure, physical object, … in SNOMED CT) so the two are aligned (by design).

the hair acts as a physical memory and integrator of mercury exposure https://www.annclinlabsci.org/content/36/3/248.full

The current NPU concept: NPU02700, Hair—Mercury; subst.cont. = ? µmol/kg does not capture that meaning.

perhaps in the information model and not in the code. The FHIR resource currently does not support this though.

Gunnar - The mercury content inheres in the hair follicles were the hair structure was created and at the time when the structure was created. This timepoint differ from the sampling time of the hair. This is utilized clinically; the mercury content of the hair might thus reflect the mercury challenge for the body one or more months prior to the sampling (depending on the hair cut + distance from scalp

The sampling is probably standardized in some way – we have to ask the experts. And this standardization ought to be included in the code.

Young Bae - 

Agree on the information is needed but in the common laboratory information model. Not in the description of the quantity.

Jim Case - Body structure is used for inheres_in for NPU-SNOMED CT project

This enables modelling location of hair from body structure hierarchy

ALL - Hair length can be another observation in FHIR observation group i.e. one observation to represent mass content of mercury in hair; and another observation to represent length of hair with a codable concept e.g. 12704-3 Length of hair

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NOTES

Mass content is deprecated in the IUPAC green book

Mass content and mass fraction are equivalent

No change required to SNOMED CT properties

NPU can map mass fraction to LOINC / SNOMED CT mass content

Mass fraction - of components (e.g. haemoglobin types)

Mass content - of the specimen (e.g. hair sample, calculus)

NPU is in agreement with LOINC for mass ratios and relative concentrations (mass or molar)

Do we expand ratios and relative concentrations in the terminology descriptions? e.g.

Ratio of mass concentration of protein to substance concentration of creatinine in urine at point in time

Ratio of mass concentration of creatinine to mass concentration of protein in urine at point in time

 Recheck expansions of descriptions of mass/mass

mol/mol

ratios with lab experts

Review the session outputs

Gunnar will come back to Karim to look at the Swedish model of microbiology post-coordination

International decision for sharing and reusing path and lab SNOMED CT observable entity content

These concepts are modelled with both inheres_in and direct_site

Farzaneh to take these back and discuss internally for a steer on the use of inheres_in for these concepts

On hold

SI propose to remove inheres_in but await formal decision from this group

colour, appearance, identification

Concept is primitive if the description is more specific than the modelling. Concept logical definition must not be more specific than concept description

LOINC uses time_aspect NPU is implied

Definition - Time of specimen collection

Must be stated consistently  in description AND modelling in accordance with SI editorial policy

modelling single point in time explicitly to enable correct classification of content

Time-specific concepts must not be subsumed by unmodelled soft default implicit 'single point in time' concepts

UK NRC to discuss applying the same principle

Inheres_in effectively duplicates direct_site. They are two different perspectives (lab and clinical) of the same target

Direct_site is suitable for sample-based diagnostics and not other areas but NPU will not be following those guidlines

In Cancer Synoptic histology - carcinoma inheres_in neoplasm, when specimen is taken, the direct_site is specimen 

LOINC and NPU share linkage via 3 attributes, as SNOMED CT concepts they will classify as siblings, because of the different use of Inheres_in and direct_site

Can compute mapping using ECL

Some challenges e.g. NPU uses units, LOINC does not

Direct_site attribute sufficiently captures specimen and derivable substance / site from specimen modelling 

LOINC Ontology to model direct_site

NPU to model inheres_in

Create interoperable rules and document in guidance 

LOINC and NPU take different approached (to be documented)

UK NRC need to decide approach

Representation of percent

Concept is primitive if the description is more specific than the modelling. Concept logical definition must not be more specific than concept description

unit not required field in LOINC so in SNOMED CT, if fully defined without unit, could generate logical equivalences 

Represent percent in the description and the unit in SNOMED CT in accordance with SI editorial policy 

LOINC Committee decided to remove 100 denominator and reflect percent as UoM. LOINC Ontology will only release codes with 'fraction property (e.g number fraction, mass fraction)' and percent will be identified by unit.

Percent unit is used with NPU. NPU is more standardised with use of units so there is less variation (e.g. for substance conc, one unit)

International content will continue to model percent unit according to cancer synoptic content - any question mark for moving to LOINC Ontology?

UK will maintain SNOMED CT percentage subtypes to support the UK labs migration from Read, modelling percent unit as standardised exceptions, but align to LOINC Ontology properties in order to compute equivalences (when combined with unit %) and classify as subtypes if needed 

Inconsistencies - International content for cancer synoptic reporting by immunohistochemistry

1255078008 | Percent of cell nuclei positive for proliferation marker protein Ki-67 in primary malignant neoplasm by immunohistochemistry (observable entity) |

Does not use percent unit in modelling

e.g. 1 - modelling time_aspect -> single point in time but not stating this in the description

In contrast to LOINC Ontology examples that do state 'at single point in time' in the description and model in the logic

e.g.2 - use inheres_in whereas LOINC Ontology used direct_site

SI are adding percent unit to the content

Awaiting formal decision on inheres_in from this group

Awaiting formal decision on time_aspect from this group

How do we represent both axes of ordinal AND qualitative / semi-q in SNOMED CT model?

NPU descriptions in this link (not complete yet): https://labterminology.com/npu-concept-model/general-rules-on-result-type/...

Hierarchies are inconsistent for qualifiers that represent the targets of scale_type defining attribute for observable entity concepts (see presentation slides)

Both are ordinal scales 

Both represented as presence in LOINC and international SNOMED CT

Semi-q needs to be defined

UK need to make a distinction between qualitative and semi-q in the terminology

Relative concentration of a substance in two different specimens

Relative concentration two different measurement properties

CALCULATIONS

Young Bae recommended we look at IUPAC relative properties and ratios

Patient test results calculations - consistent approach to reference external formulae, and not represent in SNOMED CT observable entity concept model (including ratios)

After review of the resources, internal discussions and a review with the LOINC team, we've determined that "Ratio" and "Fraction" should be classified as sibling properties.

IFCC-IUPAC Silverbook https://iupac.org/what-we-do/books/silverbook/ but also on the homepage: https://labterminology.com/list-of-kinds-of-property/