Presently, the only method available to monitor disease activity in Eosinophilic Esophagitis (EoE) is endoscopy with pathological review of biopsies. The overall goal of this study is to determine the ability of the Esophageal String Test (EST), a minimally invasive capsule based technology, to measure disease activity in children with EoE. Additionally, to determine esophageal distensibility in children presenting with EoE by using the EndoFLIP (functional luminal imaging probe) device during endoscopic procedures.

When children are scheduled to undergo an endoscopy, research assistants will contact the family to arrange for the Esophageal String Test (EST) to be performed within one week of the endoscopy. The string test involves swallowing a small capsule with a thin piece of string inside it. The string unravels as the capsule goes down into the stomach. The investigator would tape the end of the string to the child's cheek, leaving it there for one hour. At the end of the hour, the investigator would remove the string by gently pulling it out through the mouth. Prior to swallowing the EST, the patient will complete the PEESS form (Pediatric Eosinophilic Esophagitis Symptom Scores) to assess symptoms.

The endoscopy and Endoscopic Reference System (EREFs) and EndoFLIP will be performed. The EndoFLIP is a slender probe covered by a smooth long balloon that is passed into the esophagus and slowly expanded with a salt solution. After standard of care endoscopic visualization, the FLIP, a 16 cm probe (Crospon) will be placed transorally and positioned 3 cm distal to the lower esophageal sphincter. Esophageal cross sectional areas and intrabag pressure will be measured during stepwise distensions beginning with 5 mL and increasing to a maximum of 70mL or intrabag pressure of 50 mmHg is achieved, whichever comes first. FLIP is FDA-approved without age restriction and its use has been approved by our IRBs previously. Primary results will be reported as distensibility plateau (mm).

Endoscopic severity: Endoscopic esophageal appearances will be scored using a validated EoE scoring system (EREFS). Five features of EoE will be scored: Edema (0-1), Rings (0-3) Exudates (0-2), Furrows (0-1), Stricture (0-1). Results will be reported as an inflammatory score (edema, exudates, furrows) and fibrostenotic score (rings, stricture). Functional Luminal Imaging Probe (FLIP):

Inclusion Criteria:

• Provide signed and dated informed consent form.
• Willing to comply with all study procedures and be available for the duration of the study.
• Male or female, aged 7 to 18 years old, inclusive
• Undergoing upper Endoscopy with biopsy for clinical care at CHCO or CHOP
• Current or historical diagnosis of EoE, or suspected of having EoE

Exclusion Criteria:

• Known connective tissue disease, other eosinophilic disorders
• Past history of caustic injestion, esophageal surgery or other esophageal injury
• Known inflammatory bowel disease or esophageal motility disease (achalasia)
• Unwilling or unable to swallow the EST
• Oral or intravenous steroids in the preceding 60 days (not including swallowed topical fluticasone, budesonide, etc)
• Pregnancy
• Participation in a clinical study that may interfere with participation in this study

Up to 72 hours.