The investigators are seeking to enroll 8 children ages 2-18 already undergoing upper endoscopy. For the purposes of research, a peripheral blood and clean catch urine specimen will be obtained to measure plasma and urine metabolomics. The data will be used to determine if there are any key differences in the metabolite profile of subjects found to have eosinophilic esophagitis (EoE) versus non-EoE subjects. Once these metabolites are identified, the investigators will seek to enroll many more subjects for a validation phase.

Eosinophilic esophagitis (EoE) is a disorder of the esophagus triggered by food and/or environmental allergens and is characterized by symptoms of esophageal dysfunction and eosinophilia of the esophagus. The standard of care for diagnosing and monitoring EoE is with biopsies of the esophagus. There are currently no known biomarkers that correlate with the inflammatory activity of esophageal mucosa, and patients' symptoms alone are insufficient in providing a reliable assessment. Some studies report that patients with EoE may undergo endoscopy up to 11 times in one year. Finding a non-invasive biomarker would therefore be of high clinical and economic interest.

The investigators will seek to enroll 8 children ages 2-18 years already undergoing esophagogastroduodenoscopy (EGD). For the purposes of research, a peripheral blood specimen will be collected at the same time of peripheral intravenous (IV) placement, which is routinely performed for the purposes of sedation during endoscopy, thereby avoiding extra needle sticks. A urine sample will also be collected on the day of the EGD. These specimens will then be analyzed for plasma and urine metabolomics to evaluate for any derangements in EoE versus non-EoE subjects.

Risks to participants undergoing EGD are the same as they would be if they were not enrolled in the study as no additional biopsies will be taken. Risks associated with a blood draw are minimal and include some discomfort, such as lightheadedness, fainting, bruising, soreness, clotting and bleeding at the site of the needle stick, and in rare cases, infection. Collection of the urine specimen is by clean catch in only toilet-trained individuals.

This study should yield valuable information regarding plasma and urine metabolomics in EoE versus non-EoE subjects. Once this "discovery" data set is analyzed, future research could then focus specifically on those abnormal metabolites and seek to enroll many more subjects for a validation phase.

Inclusion Criteria:

1. Pediatric patients, ages 2-18 years, undergoing EGD with biopsies of the esophagus.
2. Children with known EoE will only be enrolled if his/her biopsy on the day of specimen collection demonstrates ≥15 eosinophils (eos) per high power field (hpf).

Exclusion Criteria:

1. Presence of other disorders associated with similar clinical, histological or endoscopic features, such as proton pump inhibitor (PPI)-responsive esophageal eosinophilia, esophageal eosinophilia associated with gastroesophageal reflux, Crohn's disease, infectious esophagitis (i.e. herpes simplex virus or candida), drug-associated esophagitis, collagen vascular disease, hypereosinophilic syndrome and eosinophilic gastroenteritis.
2. Children with known EoE and biopsy demonstrating <15 eos/hpf at the time of specimen collection.
3. Inability to provide a clean catch urine specimen (i.e. not toilet-trained).

Children ages 2-18 years already undergoing upper endoscopy (EGD)