Phenotype, Endotype, and Biomarker

Allergies are heterogeneous conditions that can be considered using phenotype, endotype, and biomarkers as diagnostic and prognostic criteria.

The phenotype
includes special clinical features of a disease with no direct reference to its pathogenesis and response to treatment. For example, asthma can be divided into allergic phenotype and non-allergic phenotype.

represents a phenotypic subgroup of a disease characterized by particular cellular and molecular mechanisms and therapy response. For example, there are two main endotypes of allergic asthma, Th2-high/eosinophilic endotype and Th2-low/Th17/neutrophilic endotype.

A biomarker
is a specific biological indicator of a disease's phenotype or endotype. Biomarkers are measured in various biological specimens such as blood, sputum, nasal secretion, tears, saliva, exhaled breath condensate, skin exudate, urine, biopsy, etc. Fractional exhaled nitric oxide (FeNO), blood and sputum eosinophilia, and serum total IgE are conventional biomarkers in allergic asthma.