The purpose of this study is to evaluate the relationship between fractionated exhaled nitric oxide, peripheral eosinophils, and plasma citrulline and ß-alanine in patients with eosinophilic esophagitis (EoE) compared to those without EoE.

The hypothesis is that a combination of elevated fractional exhaled nitric oxide, increased peripheral eosinophils, and elevated plasma citrulline and ß-alanine is associated with active EoE.

Inclusion Criteria:

• Pediatric patient, ages 5-18 years old, who will undergo esophagogastroduodenoscopy with biopsies at Children's Memorial Hermann Hospital, as part of the standard of care in the evaluation of EoE
• Signed informed consent by a parent or legal guardian
• Signed assent form by the child/adolescent subjects 7-18 years of age

Exclusion Criteria:

• Past medical history of active asthma, active allergic rhinitis, inflammatory bowel disease (IBD), parasitic infection, hay fever and any exposure to smoking (including secondhand smoke) because these disorders are known to affect the FeNO levels
• Active respiratory tract infections at the time of FeNO evaluation because this can affect the result of the FeNO as well
• Asthma questionnaire and/or Spirometry test consistent with asthma

All patients will be recruited from the outpatient clinic of the Pediatric Gastroenterology Division of The University of Texas Health and Science Center at Houston.