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====== Food allergy definition ======

Researchers from the [[https://www.rug.nl/staff/j.m.vonk/|University Medical Center Groningen]] developed a definition of food allergy for all Lifelines participants (adults and children) using the [[allergies|allergy variables]] from [[2A]]. ([[sections]]: [[Diseases & symptoms]] ([[Allergies]]) and [[secondary & linked variables]]).\\

The Food allergy definition can be requested in the [[https://data-catalogue.lifelines.nl/|Lifelines catalogue]].\\
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===== Background =====
In 2020, [[https://doi.org/10.1371/journal.pone.0231818|Westerlaken-van Ginkel et al.]] published a paper in which an algorithm to define food allergy in adults in Lifelines is developed and described. Since the [[allergies|allergy variables]] for adults differ slightly from those of children (completed by the parents) and adolescents, this algorithm has to be adapted to defined food allergy in children/adolescents as well. 

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===== Calculation of food allergy definition =====
The calculation of the food allergy definition consisted of three steps: 1) coding of open text variables, 2) defining and calculating criteria to define food allergy, and 3) creating the overall food allergy variables.
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=== 1. Coding of open text variables ===
At the start of the process, the responses from participants on "other allergen", "other reaction", and "other person who diagnosed the food allergy" are coded. The allergens and reactions were coded as //common//, //less common//, and //uncommon// using the tables as descibed by [[https://doi.org/10.1371/journal.pone.0231818|Westerlaken-van Ginkel et al. (2020)]]. These original coding tables were slightly changed after reachging consensus. The "other person" items have been coded into //alternative practitioner//, //other person//, and //no person mentioned//.
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=== 2. Defining and calculating criteria to define food allergy ===
For adults, five criteria are included in the questionnaire, where the answers to these should not fall in the unlikely category. The unlikely answers are:
  * **Criterium 1:** food allergy is only diagnosed by an alternative practitioner
  * **Criterium 2:** the onset of symptoms after ingesting the food is after a day or more
  * **Criterium 3:** the amount of food that elicits the reaction is a normal portion or more
  * **Criterium 4:** the duration of the symptoms is longer than 1 week
  * **Criterium 5:** a negative double blind placebo controlled food provocation test
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=== 3. Creating overall food allergy variables ===
Food allergy was coded as //no food allergy (0)//, //indeterminate food allergy (1)//, and //likely food allergy (2)// according to the flow diagram provided in the paper of [[https://doi.org/10.1371/journal.pone.0231818|Westerlaken-van Ginkel et al. (2020)]].

For children and adolescents only the two criteria have been asked. As a result, the food allergy definition is based on these two criteria only.For adults, it was decided to include two additional definitions of food allergy:
  - A version without incorporating criterium 3 as there were many participants who reported a likely allergen and a likely reaction while the other four criteria were not unlikely.
  - A version including only criterium 1 and 2, to make the definition comparable to the one for children and adolescents.
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=== Remarks from the UMCG researchers ===
  - If a participant has two different questionnaires available, the quetsionnaire with the highest score on food allergy is selected.
  - If a researcher wants to investigate food allergy in both children/adolescents and adults it is recommended to use //foodallergy_score_all_c_1//. If a researcher wants to investigate food allergy in adults only, it is recommended to use //foodallergy_score_adu_c_2// and use the //foodallergy_score_adu_c_3// variable in a sensitivity analysis.
  - In the future the type of foods and the type of reactions will be classified and added.
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===== Variables =====
| **Label English**                                                                                                                                                         | **Label Dutch**                                                                                                                                                                              | **Code**                      | **Variable**        | **Assessment**  | **Age**  |
| age at definition of food allergy (based on questionnaire)                                                                                                                | leeftijd ten tijde van definitie voedselallergie (op basis van moment vragenlijst)                                                                                                           | foodallergy_age_all_c_1       | agefa               | sec *           | all      |
| reported product is likely allergenic?                                                                                                                                    | gerapporteerd product is waarschijnlijk allergeen?                                                                                                                                           | foodallergy_allergen_ach_c_1  | likelyallergen_ach  | sec *           | all      |
| reported product is likely allergenic?                                                                                                                                    | gerapporteerd product is waarschijnlijk allergeen?                                                                                                                                           | foodallergy_allergen_adu_c_1  | likelyallergen_adu  | sec *           | all      |
| reported product is likely allergenic?                                                                                                                                    | gerapporteerd product is waarschijnlijk allergeen?                                                                                                                                           | foodallergy_allergen_chi_c_1  | likelyallergen_chi  | sec *           | all      |
| reported reaction is likely allergic?                                                                                                                                     | gerapporteerde reactie is waarschijnlijk allergisch?                                                                                                                                         | foodallergy_reaction_ach_c_1  | likelyreaction_ach  | sec *           | all      |
| reported reaction is likely allergic?                                                                                                                                     | gerapporteerde reactie is waarschijnlijk allergisch?                                                                                                                                         | foodallergy_reaction_adu_c_1  | likelyreaction_adu  | sec *           | all      |
| reported reaction is likely allergic?                                                                                                                                     | gerapporteerde reactie is waarschijnlijk allergisch?                                                                                                                                         | foodallergy_reaction_chi_c_1  | likelyreaction_chi  | sec *           | all      |
| presence of food allergy according to criteria 1 and 2 (excluding criteria 3: amount of food eliciting reaction, 4: duration of symptoms, and 5: result dbpcfc)           | aanwezigheid van voedselallergie volgens criteria 1 en 2 (exclusief criteria 3: hoeveelheid voedsel dat reactie uitlokt, 4: duur van symptomen, en 5: resultaat dbpcfc)                      | foodallergy_score_ach_c_1     | foodallergy_ach     | sec *           | all      |
| presence of food allergy according to criteria 1 and 2 (excluding criteria 3: amount of food eliciting reaction, 4: duration of symptoms, and 5: result dbpcfc)           | aanwezigheid van voedselallergie volgens criteria 1 en 2 (exclusief criteria 3: hoeveelheid voedsel dat reactie uitlokt, 4: duur van symptomen, en 5: resultaat dbpcfc)                      | foodallergy_score_adu_c_1     | foodallergy3_adu    | sec *           | all      |
| presence of food allergy according to criteria 1, 2, 4, and 5 (excluding criteria 3: amount of food eliciting reaction)                                                   | aanwezigheid van voedselallergie volgens criteria 1, 2, 4, en 5 (exclusief criteria 3: hoeveelheid voedsel dat reactie uitlokt)                                                              | foodallergy_score_adu_c_2     | foodallergy2_adu    | sec *           | all      |
| presence of food allergy according to criteria 1, 2, 3, 4, and 5                                                                                                          | aanwezigheid van voedselallergie volgens criteria 1, 2, 3, 4, en 5                                                                                                                           | foodallergy_score_adu_c_3     | foodallergy_adu     | sec *           | all      |
| presence of food allergy based on [foodallergy_score_adu_1] and [foodallergy_score_ach/chi_c_1], with the highest score shown in case of multiple scores per participant  | aanwezigheid van voedselallergie gebaseerd op [foodallergy_score_adu_1] en [foodallergy_score_ach/chi_c_1], met de hoogste score weergegeven in het geval van meerdere scores per deelnemer  | foodallergy_score_all_c_1     | fa3                 | sec *           | all      |
| presence of food allergy based on [foodallergy_score_adu_2] and [foodallergy_score_ach/chi_c_1], with the highest score shown in case of multiple scores per participant  | aanwezigheid van voedselallergie gebaseerd op [foodallergy_score_adu_2] en [foodallergy_score_ach/chi_c_1], met de hoogste score weergegeven in het geval van meerdere scores per deelnemer  | foodallergy_score_all_c_2     | fa2                 | sec *           | all      |
| presence of food allergy based on [foodallergy_score_adu_3] and [foodallergy_score_ach/chi_c_1], with the highest score shown in case of multiple scores per participant  | aanwezigheid van voedselallergie gebaseerd op [foodallergy_score_adu_3] en [foodallergy_score_ach/chi_c_1], met de hoogste score weergegeven in het geval van meerdere scores per deelnemer  | foodallergy_score_all_c_3     | fa                  | sec *           | all      |
| presence of food allergy according to criteria 1 and 2 (excluding criteria 3: amount of food eliciting reaction, 4: duration of symptoms, and 5: result dbpcfc)           | aanwezigheid van voedselallergie volgens criteria 1 en 2 (exclusief criteria 3: hoeveelheid voedsel dat reactie uitlokt, 4: duur van symptomen, en 5: resultaat dbpcfc)                      | foodallergy_score_chi_c_1     | foodallergy_chi     | sec *           | all      |

* The food allergy definition variables are included as assessment 'sec' because they link to different questionnaires from assessment [[2A]].
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