**6. Diagnostic tests**

#### **6.1 Laboratory (lab) tests**

There is no single Lab test that can support the diagnosis of EoE. Mild peripheral eosinophilia may or may not be present. Peripheral eosinophilia, elevated serum eosinophilderived neurotoxin and eotaxin3 (CCL26) may have the potential to act as a biomarker for monitoring EoE [22].

#### **6.2 Endoscopy**

The esophageal mucosa may look normal in 7–10% of cases of EoE [23]. A variety of nonspecific features of inflammation can be seen in EoE during endoscopy. The five major endoscopic features of EoE as per EoE endoscopic reference score (EREFS) are edema, rings (**Figure 3**), exudates, furrows and strictures [24]. Edema is identified by loss of vascular markings and mucosal pallor. Transient concentric rings or trachealization may indicate esophageal longitudinal muscle contraction [25] and fixed rings may indicate fibrous stricture formation due to tissue remodeling. Exudates or white spots or white plaques may mimic candida esophagitis, histologically they are eosinophilic microabscesses. Furrows are vertical lines running parallel to the axis of the esophagus probably due to epithelial edema.

**Figure 3.** *Endoscopy showing multiple esophageal rings.*

Chronic eosinophilic esophagitis may lead to long segment or short segment stricture. Narrowcaliber esophagus due to luminal narrowing of most of the esophagus is infrequently seen in EoE. Crepe paper esophagus occurs due to esophageal mucosal fragility and is recognized by a mucosal tear that occurs during passage of a diagnostic endoscope but neither during endoscope withdrawal nor after esophageal dilation. Although more than one of the above endoscopic findings can be seen in the same patient, none of them is specific for EoE. Recently, esophageal "pull" sign (substantial resistance and mucosal tenting during pulling of the biopsy forcep) was found to be highly specific and responsive to successful therapy in EoE patients [26].

Current recommendation is to take at least 2 to 4 biopsies from both proximal and distal halves of the esophagus (5 cm above GE junction) and also to take targeted biopsies from abnormal mucosa, *i.e.,* exudates, rings, edema, furrows and strictures. Gastric and duodenal biopsies should also be taken to evaluate eosinophilic gastroenteritis.
