Table 1.

Biomarkers for biological therapies

Biologic	Criteria for prescriptiona	Limitations	References
Omalizumab (anti- IgE)	•Serum IgE >30, <1500 IU/m •Sensitization to perennial aeroallergens •FeNO ≥19,5 ppb b •Eosinophils ≥260/mm3 b •Periostin ≥50 ng/mL b •Decreased FEV1	•IgE assays are not able to distinguish between the omalizumab–IgE complex and free IgE •Eosinophil levels are influenced by infections, allergen exposure, and steroid therapy •FeNO levels are transiently influenced by exercise and prior spirometry. Inhaled and systemic steroids, and leukotriene-receptor antagonists reduce FeNO, and high nitrate food may increase it. It increases at a rate of 5 % per year of age due to increased height. •Periostin level is influenced by bone metabolism	17,27,32, 33, 34, 35, 36, 37, 38
Mepolizumab (Anti-IL5)	Blood eosinophil count ≥300 cells/μL, or blood eosinophil count ≥150 cells/μL in patients with well characterized eosinophilic asthma or requiring regular OCS	•Peripheral blood eosinophil counts do not always reflect airway eosinophilia •Eosinophil levels are influenced by infections, allergen exposure, and steroid therapy	17,27,37, 38, 39, 40, 41
Benralizumab (anti-IL5 Ra)	Blood eosinophil ≥300/μL
Dupilumab (Anti-IL4R)	Peripheral eosinophilia (≥150 cells/μL), and/or FeNO >25 ppb	•Peripheral blood eosinophil counts do not always reflect airway eosinophilia	17,37, 38, 39, 40, 41, 42
Tezepelumab (anti-TSLP)	•Blood eosinophil ≥300/μL •FeNO ≥25 ppb	•Eosinophil levels are influenced by infections, allergen exposure, and steroid therapy •FeNO levels are transiently influenced by exercise and prior spirometry. Inhaled and systemic steroids, and leukotriene-receptor antagonists reduce FeNO, and high nitrate food may increase it. It increases at a rate of 5 % per year of age due to increased height.	32,43

FeNO: fractional exhaled nitric oxide; FEV1: forced expiratory volume in 1 s; ppb: part per billion; TSLP: thymic stromal lymphopoietin.

^aIn addition to the diagnosis of severe asthma.

^bWould predict better response.