Abstract
Wheezing is one of the characteristic symptoms of asthma, but all preschool children with wheezing are not diagnosed with asthma. Preschool children are not cooperative enough to participate in spirometry and invasive tests. Thus, there is no conventional method to diagnose asthma in preschool children. We reviewed studies on non-invasive biomarkers for assessing asthma in preschool children. Specimens that can be easily obtained by non-invasive methods are blood, exhaled breath and urine. Eosinophils, eosinophil cationic protein and eosinophil-derived neurotoxin (EDN) in blood are helpful in evaluating eosinophilic inflammation of the airways. Exhaled breath contains nitric oxide, volatile organic compounds, various cytokines and mediators as analytical components. Fraction of exhaled nitric oxide has been used to assess the degree of eosinophil inflammation and has been standardized in school-age children and adults, but not yet in preschool children. Exhaled breath condensate (EBC) pH and various cytokines/mediators that are detected in EBC seem to be promising biomarkers for assessing asthma, but need more standardization and validation. There are several biomarkers useful for assessing asthma, but none are ideal. Some biomarkers need standardized methods of obtaining samples from uncooperative preschool children for clinical use and require sufficient validation. Recently, another activated eosinophil marker, serum EDN, has shown promising results as a biomarker for recurrent wheezing and asthma in preschool children.