The use of a home rapid test for the detection of both gluten immunogenic peptides (GIP) in urine and immunoglobulin A (IgA) anti tissue transglutaminase (anti-tTG) antibodies in blood may contribute to the early detection of volunteers who suffer celiac disease (CD), a highly under-diagnosed disorder. Patients with positive results could inform their doctors in order to accelerate the diagnosis, contribute to symptoms control and improve their quality of life.

This observational, cross-sectional study with no interventions applied in subjects consists on a single group of volunteers between 2 and 18 years old. They will be given an informed consent which must be signed by them or their parents/legal guardians, a Celiac Symptoms Index (CSI) questionnaire and the sample collection material required on the testing day. Urine samples will be collected and analysed in situ or alternatively they will be stored and analyzed after at the laboratory. Blood samples will be collected and analyzed in situ the testing day.

The main outcome is to determine the prevalence of CD through mass screening within the pediatric and adolescent population in order to provide an early diagnosis and avoid long-term consequences which are suffered by untreated patients. As an international innovation, misdiagnosis (false negatives) because of an insufficient gluten intake are expected to be detected, thus the use of GIP detection in urine will confirm gluten ingestion at the diagnosis. Volunteers with a confirmed diagnosis of CD could be monitored by their doctors to corroborate whether a gluten-free diet improves their quality of life.

Hypothesis: the use of a home rapid test for the detection of both gluten immunogenic peptides (GIP) in urine and IgA anti-tTG antibodies in blood may contribute to the early detection of volunteers who suffer celiac disease (CD), a highly under-diagnosed disorder. Patients with positive results could inform their doctors in order to accelerate the diagnosis, contribute to symptoms control and improve their quality of life.

Objectives:

Primary objective: to perform a mass screening in the pediatric and adolescent population (2 - 18 years old) in order to assess the prevalence of the CD providing early diagnosis of possible patients through 1 - Detection of IgA anti-tTG antibodies present in blood (to be measured by home rapid tests); 2 - Detection of GIP in urine (to be measured in situ or at a central laboratory).

Specific objectives: 1- To determine the prevalence of CD, particularly in children between 2 and 18 years old; 2 - To detect possible hidden CD cases, avoiding future irreversible damages by a late detection of this pathology such as growth impairment, decalcification, neurotoxicity or risks of suffering other autoimmune diseases; 3 - To detect misdiagnosis (false negatives) because of an insufficient gluten intake, as an international innovation.

Study design: this observational, cross-sectional study with no interventions applied in subjects consists of a single group of volunteers between 2 and 18 years old. They will be given an informed consent which must be signed by them or their parents/legal guardians, a Celiac Symptoms Index (CSI) questionnaire, a short clinical questionnaire and the sample collection material required on the testing day. Urine samples will be collected and analysed in situ or alternatively they will be stored and analyzed after at the laboratory. Blood samples will be collected and analyzed in situ the testing day.

Study participants: volunteers from the pediatric and adolescent population between 2 and 18 years old. Gluten consumption previous to testing is an innovative requirement in order to validate the IgA anti-tTG antibodies rapid test.

Study procedure:

1. Patient enrollment.
2. Testing day: all participants will 1 - return the informed consent signed by them or their parents/legal guardians; 2 - complete the Celiac Symptoms Index (CSI) questionnaire and the clinical questionnaire to check if they have had any previous symptoms or other relevant information to be considered; 3 - collect urine samples in order to determine GIP presence through a immunochromatographic test (iVYCHECK GIP Urine, Biomedal S.L., Seville, Spain) in situ or at the central laboratory, therefore samples will need to be stored. It may be confirmed whether the volunteer was ingesting gluten when the test was performed. - A. If the result is positive, a serological test will be performed at a certified laboratory in order to confirm the volunteer's disease and a specialist to perform the diagnosis will be recommended. Whether the diagnostic is confirmed, five GlutenDetect's units will be given to each diagnosed volunteer to make sure they can check whether the diet is properly followed. - B. If the result is negative, the possibilities of suffering CD are low so any additional test will be performed. Exceptionally, those whose gluten level in urine is undetectable, but their CeliacDetect result appears as negative, a deeper study will be performed about gluten ingestion the day before through 24 hours recall.

Number of participants: a minimum of 1000 volunteers would be needed to achieve a conclusive study in order to determine at least 10 cases of CD. The calculation was made according to CD's prevalence of 1% described by several studies.

Measurements: 1- Laboratory rapid test (iVYCHECK GIP Urine, Biomedal S.L., Seville, Spain) for GIP determination in urine samples and immunochromatographic rapid test (CeliacDetect, Biomedal S.L., Spain) for IgA anti-tTG antibodies detection in blood; 2- CD related symptoms (CSI questionnaire). Urine samples will be analysed in situ or stored and analyzed later at a central laboratory (Biomedal S.L., Seville, Spain).

Statistical analysis: the data obtained in the study will be collected in a data base created with this purpose. Variables are tabulated through the IBM SPSS Statistics V25.0 program from International Business Machines (IBM) (Armonk, New York, USA). Different study variables will be considered: 1 - related to patients (age, gender, parent's study level); 2 - related to the "Celiac symptoms index" questionnaire (presence or not of previous symptomatology); 3 - related to samples (GIP presence in urine and IgA anti-tTG antibodies presence in blood). Each test's result will be considered as significant if the value p<0,05 and very significant if p<0,01. A confidence of 95% will be taken for intervals. When p>0,05, the result will be considered as non-significant.

Inclusion Criteria:

• Children and adolescents volunteers (2-18 years old).
• Regular gluten consumption.
• Willingness to perform the study and ability to collect urine samples.
• The signing of the informed consent by the volunteer and his/her legal guardians.

Exclusion Criteria:

• Related diseases or psychiatric alterations which do not recommend being included in the study as the researcher's consideration.
• Lack of foreseeable collaboration.
• Patients which do not provide samples or surveys in 70% of cases.

Population comprised of patients between 2 and 18 years old who are diagnosed with celiac disease or suspected to suffer the disease. They should have willingness to perform the study and ability to collect urine samples. Moreover, the patients or their legal guardians have to sign the informed consent.