2.3 Kind of Property

The second part of the fully specified name distinguishes between different kinds of quantities relating to the same substance, e.g., the mass concentration versus the substance (molar) concentration of sodium in a urine sample, or the absolute eosinophil count versus the percent of the total white count that is made up of eosinophils. The type of Property (kind of quantity) is an IUPAC concept described in the Silver Book.[[^21]] We include most of the relevant IUPAC quantitative Property types in LOINC. We also have a set of Properties, such as PrThr (Presence or Threshold), Type, Seq (nucleotide sequence), and Loc (geographic location), that are used in qualitative terms. More examples of Properties are given in Table 8. The complete set of active LOINC Properties is available in the LOINC Part File and can be identified because they contain a PartTypeName of PROPERTY.

In Version 2.75, August 2023, the semi-quantitative (SemiQn) scale was re-introduced for non-continuous measurement of numeric values. This new scale option has an impact on categorizing PROPERTY. Mass and substances concentration properties need scrutiny to determine whether the measurement was on a continuous linear calibration or if ranges/buckets of non-continuous, non-overlapping values were made and being reported. For this reason, properties such as Mass and Substance concentrations are represented under BOTH quantitative and semi-quantitative sections.

2.3.1 Quantitative Properties

2.3.1.1 Main quantitative Property categories

Mass: Observations reported with mass (milligrams, grams, etc.) in the numerator of their units of measure have Properties that begin with the word mass: mass content, mass concentration, etc.

Substance: Observations reported with moles or mill equivalents in the numerator of their units of measure have Properties that begin with the word substance.

Catalytic activity: Observations that report enzymatic activity have Properties that begin with catalytic, e.g., catalytic concentration, catalytic content.

Arbitrary: Results that report arbitrary units in the numerator of their units of measure have a Property that begins with arbitrary.

Number: Counts are associated with Properties that begin with “number”, e.g., a white blood cell count reported as a number of WBCs divided by volume of blood, would have a Property of number concentration.

2.3.1.2 Quantitative Property category subtypes

Each of the above major Property categories has number of derivatives: concentration, content, ratio, fraction, and rate (see LOINC properties table (Table 8)).

Concentrations: An amount divided by a volume. These have units such as mg/dL, or gm/L.

Contents: An amount divided by a mass. These have units such as mg/gm sample or mg/total protein.

Ratios: When a result is reported as one measure divided by another taken from the same System, the Property is a ratio. The ratio of the mass concentration of substance A divided by the mass concentration of creatinine in a urine sample, for instance, is a mass ratio (MRto). The numerator and denominator of a ratio must come from the same System. If the measures come from different specimens, e.g., PT patient/PT control or creatinine serum vs. creatinine urine, it is a relative ratio (RelRto). The ratio of times coming from an actual and normal control (as in some coagulation tests) will be relative time (RelTime), a ratio of mass concentrations coming from two different specimens will be relative mass concentration (RelMCnc), and a ratio of catalytic concentrations from different specimens will have the property of relative catalytic concentration (RelCCnc).

Fractions: Fractions are ratios of a part over a whole: Creatine kinase.MB/Creatine kinase.total, if measured in grams, is a mass fraction (MFr). Fractions are usually reported as percent. In Canada and other countries, fractions are measured as pure decimal fraction. For instance, a 95% O2 saturation would be resulted as 0.95. For some Analytes, both styles of reporting are used in Canada, so we were asked to distinguish decimal fractions from pure fractions. Beginning with the June 2012 release, we now include terms that have .DF appended to the existing fraction properties. For example, some terms now have properties of MFr.DF, SFr.DF, VFr.DF, etc. Because of the confusion that occurs in countries that report results as both decimal fraction and percent, these properties were created to represent decimal fractions that are reported without units.

Rates: A rate is a measure per a time period, e.g., mg/day would be a mass rate (MRat). Clearances have the Property of volume rate, but “Clearance” will be included in Analyte name to clarify meaning, for example:

Sodium renal clearance:VRat:24H:Urine:Qn:

Some measures do not fit the above schema. For instance, IUPAC describes an entitic quantity. This refers to measure per entity (e.g., cells, receptors, and molecules). Entitic quantities usually have units that include the name of some entity, e.g., red blood cells (“per 106 RBCs”).

One must be careful when mapping measures of constituents of red blood cells to LOINC code because they can be expressed many ways, e.g., as an amount “per mass of hemoglobin”, “per liter of blood” or “per red blood cell”. The first is a mass content, the second a mass concentration, and the last is an entitic mass (mass per entity) — all different properties.

The pharmaceutical industry has the need for laboratory terms that are not specific as to whether the test measures a substance (substance concentration or substance rate) or mass (mass concentration or mass rate). We have created terms with the properties of MSCnc or MSRat to represent these more general test observations. By default, both RELMA and the online search application (http://search.loinc.org) hide these terms from the search results, but they can be displayed by adjusting the search limit settings in these programs.

Some tests report the name of an organism (or initially report the presence of any organism, and later identify the particular strain), toxic substance, antibody or antigen, as a test result. Use Prid (presence or identity) as the type of Property field for results of this sort.

Examples:

Bacteria identified:Prid:Pt:Isolate:Nom:Bacterial subtyping

Barbiturates positive:Prid:Pt:Urine:Nom:Confirm

2.3.1.2.1 Arbitrary Concentration (ACnc)

ACnc means the number of arbitrary units in a volume (arbitrary concentration). We originally used ACnc as a “temporary” place-holder for observations with ordinal answers. We then transitioned to replacing ACnc with either Pr (for results simply based on whether the Analyte is present or not without being determined by a cut off value) or Threshold (for observations reported as “positive” or “negative” based on an internal threshold or cut off). As we updated existing terms with the new model, in many cases it was difficult to definitively know how results were determined. Therefore, as of release 2.56, we are using a single Property of PrThr to represent results based on either the presence or absence of an Analyte regardless of whether or not it is based on an internal cut off. This change was approved by the Laboratory LOINC Committee in June 2016.The display name will continue to say Presence. All of the existing terms with a Property of ACnc, Pr or Threshold and a Scale of Ord were updated to have the Property PrThr for the 2.56 release. A single term with Property ACnt and Scale Ord was also updated to have the Property PrThr.

Examples:

Clonazepam:PrThr:Pt:Ser/Plas:Ord:

Hepatitis B virus surface Ag:PrThr:Pt:Ser/Plas:Ord:Confirm

Burkholderia mallei:PrThr:Pt:XXX:Ord:Organism specific culture

VKORC1 gene.c.1173C>T:PrThr:Pt:Bld/Tiss:Ord:Molgen

The Property of Prid will continue to be used when the result is selected from a list of organisms, as described above.

2.3.2 Semi-quantitative Properties

Mass: Observations reported with mass (milligrams, grams, etc.) in the numerator of their units of measure have Properties that begin with the word mass: mass content, mass concentration, etc. with a method of Test Strip. Assays measuring in mass concentration on a non-continuous numeric Examples include mass or molar concentrations detected by chromogenic changes on a test strip. The changes in color indicate intervals of concentration, such as 2, 4, 8, and 12 mg/dL of urobilinogen.

Substance: Observations reported with moles or mill equivalents in the numerator of their units of measure have Properties that begin with the word substance with a method of Test Strip Assays measuring in substance concentration on a non-continuous numeric Examples include mass or molar concentrations detected by chromogenic changes on a test strip. The changes in color indicate intervals of concentration, such as 2, 4, 8, and 12 mg/dL of urobilinogen.

Titer: Titers are another example of discrete values reported serially eg 1:8, 1:16 but not all values sequentially are reported. The true concentration may have been 1:9, but the measurement of 1:8 implies a true measure between 1:8 and 1:16.

Percentile: Percentiles are varying thresholds distributing values into buckets under 100. The difference between the 20th and 25th percentiles are only the values within the 21st, 22nd, 23rd, 24th and 25th brackets. Examples include types of lipid distributions amongst a general population’s findings.

NCNCRange: Created in 2019 for molecular level quantitation of infectious microorganisms, this property is used for very large ranges of numeric formats. Examples include measurement of microorganism DNA reported in ranges such as < 10^3 copies/mL; 10^3 – 10^4.5 copies/mL; 10^4.5 – 10^5 copies/mL.

ScoreRange: With repeated measurements of a patient, a confidence interval is an example of ScoreRange property.

Arbitrary Concentration: When used to report test strip values, such as Ehrlich units that are segregated into buckets, ACNC can be used as a semi-quantitative property.

Numeric Concentration: When used to report test strip values, such as Leukocytes and Erythrocytes, NCNC can be used as a semi-quantitative property.

Relative Density: When used to report test strip values, such as Specific Gravity, RelDen can be used as a semi-quantitative property.

2.3.3 Qualitative Properties

Qualitative Properties describe what is being measured for non-quantitative laboratory and clinical concepts. Such Properties describe a wide variety of results, such as whether or not an analyte is present, the specific type of analyte detected, a person’s address, telephone number, or e-mail address, or a clinical finding. Three of the most common qualitative Properties in LOINC are PrThr, Prid, and Type. These specific Properties are often confusing to LOINC users, so they are described in more detail in this section.

2.3.3.1 PrThr

The Property PrThr stands for “Presence or Threshold”, meaning either a) the actual presence or absence of an analyte, or b) that the amount of analyte detected is over some predetermined threshold.

2.3.3.2 Prid

Prid, which stands for “Presence or identity”, is used for assays that detect whether or not an analyte of a particular kind is present, and if it is, to identify the specific analyte. One example of an assay that would be represented by a LOINC term with Property Prid is a bacterial culture. When a culture is performed, it is not known in advance whether or not any bacteria will be present. Therefore, one possible result for a bacterial culture is “No growth”. But, if one or more types of bacteria are determined to be present, then the specific identity (e.g. Staphylococcus aureus) is determined and reported.

2.3.3.3 Type

The Property Type is used for assays that identify the specific analyte in cases when the baseline presence of the analyte is known. For example, if an isolate known to contain Streptococcus pneumoniae is further analyzed to determine the specific serotype, the serotype assay would have a Property of Type, not Prid, because the presence of the Streptococcus is already known.

2.3.4 More examples of LOINC Properties

Correct assignment of Property tends to be the most difficult task for new users of LOINC. Section 4 describes more information about Properties for clinical terms, and Appendix E provides more explanation and many detailed examples.

Table 8: Example LOINC Properties

* = from IUPAC Silver Book

[[^21]]: International Union of Pure and Applied Chemistry/International Federation of Clinical Chemistry. The Silver Book: Compendium of terminology and nomenclature of properties in clinical laboratory sciences. Oxford: Blackwell Scientific Publishers; 1995.