Disclosed are methods of diagnosing and treating a subject with active or inactive eosinophilic esophagitis (EoE). The methods may include the steps of detecting whether a level of eosinophil lineage-committed progenitor (EoP) is elevated in a blood sample obtained from a subject, diagnosing the subject with active EoE when an EoP level in the sample is elevated above a pre-determined cut-off value and diagnosing the subject with inactive EoE when the EoP level in the sample is below a pre-determined cut-off value; and treating the subject diagnosed with active EoE. Kits related to same are also disclosed.