The allergy testing industry provides tests for more than 450 different allergens today. Most testing detects IgE antibodies against these allergens. For some allergens testing for IgG and IgA antibodies are available, as well.
For LOINC terms that represent allergen testing, the Component is the allergen name plus the type of the antibody (mostly IgE). Most allergens relate to animals, plants or derivatives of such entities. In the past (prior to LOINC version 2.04), we used the common name, rather than the scientific name to identify the allergen. However, this approach led to some duplicate term definitions, because two different companies would name the same allergen differently. It also led to ambiguity because two different species of animal or plant would sometimes have the same common name. As of version 2.04, we corrected these problems. To help reduce the ambiguity we now use the Latin name of the species of the biologic entity that causes the allergy.
Some background: First, most allergens can also be identified with a special 2-5 character code assigned by Pharmacia[[^28]] that most allergy testing companies reference in their catalog of testing. We used these codes to identify duplicate and ambiguous LOINC allergy test terms. These Pharmacia codes are also included in the related names field of the database. Second, allergen tests are often reported in two styles: a quantitative raw measure and an ordinal (0-6) severity rank (RAST class). LOINC defines separate terms for each of these reporting styles. For example, the two LOINC codes for reporting IgE antibodies to Japanese Millet are:
Echinochloa crus-galli Ab.IgE:ACnc:Pt:Ser:QnEchinochloa crus-galli Ab.IgE.RAST class:ACnc:Pt:Ser:OrdThe RAST class is a categorization of the raw measurement based on specific allergy criteria. The specific IgE class result values (0, 1, 2, 3, 4, 5, or 6) are an ordered categorical response rather than a continuous numeric scale, therefore “RAST class” terms have an ordinal (ORD) Scale.
Laboratories also test mixtures of allergens to produce one result. An example of how these tests are represented is shown for LOINC 23797-4:
(Acer negundo+Quercus alba+Ulmus americana+Populus deltoides+Carya pecan) Ab.IgE:ACnc:Pt:Ser:Ord:MultidiskRelated name: tx2
There may be more than one type of allergen for each plant. For instance, IgE antibodies can develop towards tree pollen and the fruit of the same tree. Similarly, antibodies exist for grain and for grain pollen. In these cases, the LOINC Component will contain the word POLLEN to distinguish the pollen allergen from the food allergen. For example, the LOINC term for corn (maize) IgE antibody would be:
Zea mays Ab.IgE:ACnc:Pt:Ser:QnRelated names: f8; cultivated corn; maize
Zea mays pollen Ab.IgE:ACnc:Pt:Ser:QnRelated names: g202: cultivated corn; maize
3.11.1 Naming rules for allergens
The Component (Analyte) for an allergen consists of the name of the biologic organism that is the source of the allergen. The formal name will use the Latin taxonomic name e.g. Arachis hypogaea. The Long Common Name will use the common name of that entity, e.g., Peanut, if one exists.
In the case of very well specified allergens, the Component will also indicate whether the allergen has a natural source or has been generated via recombinant method by adding the word, native or recombinant, respectively. Different antigens from the same species are distinguished by the addition of a sequence number that roughly reflects when in time they were identified.
So you will see names that contain content like the following:
- Arachis hypogaea recombinant 1
- Arachis hypogaea recombinant 3
- Arachis hypogaea native 1
- Arachis hypogaea native 3
However, as is true in other classes of LOINC, we sometimes embed synonyms within the allergen Analyte name to help users recognize the term by their naming rules. Using the LOINC-wide convention, synonyms are enclosed in parentheses and immediately follow the word or words which they represent. We insert standard acronym names used by most allergen manufacturers as synonyms. These begin with lower case “n” or “r” to distinguish native from recombinant allergens followed by the first 3 letters of the genus (in Latin), a space and the first letter of the species (in Latin). If the first 3 letters of the genus and the first letter of the species are not enough to distinguish between two allergens, the second letter of the species name is added (e.g., Prunus avium recombinant (rPru av) 1). Because the content in the parentheses represents the antigen acronym and not the Pharmacia code, the antigen sequence number is purposely placed after the closed parenthesis. Of course we also append Ab.IgE to the end of this entity name.
Putting this all together formal and common name for the Component for the allergens listed above become:
| LOINC code | Formal name of component | Long common name of component |
|---|---|---|
| 58779-0 | Arachis hypogaea recombinant (rAra h) 1 Ab.IgE | Peanut recombinant (rAra h) 1 IgE Ab |
| 58777-4 | Arachis hypogaea recombinant (rAra h) 3 Ab.IgE | Peanut recombinant (rAra h) 3 IgE Ab |
| 65769-2 | Arachis hypogaea native (nAra h) 1 Ab.IgE | Peanut native (nAra h) 1 IgE Ab |
| 65771-8 | Arachis hypogaea native (nAra h) 3 Ab.IgE | Peanut native (nAra h) 3 IgE Ab |
With LOINC version 2.75, August 2023, the RAST class subcomponent was moved from Analyte to Method fields. RASTs are interpreted by upper and lower boundaries of measurements into six classes, according to this source. Accompanying this change was the introduction of the SemiQn scale, which is more appropriate for interpreting 0-6 classes.
[[^28]]: ImmunoCAP Allergens [Internet]. Uppsala(Sweden): ImmunoCAP; c2006 [updated 2007 November 2; cited 2008 June]. Available from: http://www.phadia.com/en-GB/5/Products/ImmunoCAP-Allergens/