Previous studies have showed that Coeliac Disease (CD) prevalence is significantly higher in children compared with adults. The largest epidemiologic study carried out in Spain to date (n=4230) reported a higher CD prevalence in children (1:71) than in adults (1:357) during 2004-2007. To study whether this difference was due to environmental factors influencing infancy or the development of gluten tolerance with age, a natural history study in pediatric age was initiated in 2013. Unexpectedly, the prevalence in children of 1-2 years of age was lower (1:135) than the previously reported in 2004-2007 for that age group (1:25). During follow-up, 1/3 of the asymptomatic cases showed reversion of the intestinal lesion and/or negativization of CD serological markers while continuing on a gluten-containing diet. Therefore, the development of gluten tolerance seems to have a major effect in age-related differences in CD prevalence. However, gluten tolerance phenomenon does not explain the differences found between the 2013-2019 and the 2004-2007 cohorts, suggesting that environmental factors may contribute as well. Apart from genetic factors, several environmental factors are believed to influence disease appearance, such as the time that gluten is introduced to the diet, viral infections, type of birth, antibiotic treatments, etc. Therefore, development of tolerance and environmental factors seem to equally play an important role in age-related differences in CD prevalence. However, more data is needed in order to know how environmental factors influence disease prevalence in Spain. Also, the previous studies carried in Spain were performed in specific geographical areas: Asturias, Basque Country and Catalonia using slightly different methodology and focused on different age groups, thus making results comparison and global extrapolation challenging.

In this study, the investigators aim to determine global CD prevalence in Spain during 2020-2021 and: 1) compare it with the results obtained in previous studies; and 2) identify whether there are any differences associated with age, environmental factors and/or geographical area. For this purpose: a) participants are recruited based on the reference population regarding age and gender; b) recruitment is done in 5 different geographical areas in Spain: Andalusia, Asturias, Basque Country, Catalonia and Madrid; c) relevant clinical, social and environmental data is collected and d) serologic screening (anti-tissue transglutaminase (tTG) - Immunoglobulin A (IgA) antibodies detection in blood serum) with histological confirmation (small-intestinal biopsy) is used to detect CD cases and determine disease prevalence.

Inclusion Criteria:

• Age 1 to ≥80 years old

Exclusion Criteria:

• Heart failure or unstable ischemic cardiopathy
• Chronic obstructive pulmonary disease or respiratory insufficiency
• Coagulopathy
• Diabetes mellitus type II with vascular complications
• Hepatic cirrhosis
• Kidney failure (Creatinine >1.5 mg/dL o glomerular filtration <30 ml /min)
• Active neoplasm
• Pregnancy
• Gluten-free diet without CD diagnosis

Participants are selected from ambulatory minor surgery departments of the pediatric and general tertiary referral hospitals in Spain. Regarding age and sex, inclusion is done reproducing the reference population of each participating Spanish regions (according to data from the Spanish Statistics Institute).