There are several factors that make diagnosing asthma particularly difficult in preschool children. Issues that complicate objective diagnosis include:
- Preschool children are unable to perform reliable spirometry
- The natural history of wheezing at preschool age is variable and harder to predict in the individual, but the majority of patients will have symptoms that improve or resolve over time
- The likelihood of an alternative diagnosis for ‘wheeze’ in preschool is relatively high, particular in cases of severe symptoms (e.g. airway malacia, congenital lung/airway malformations, reduced immune function, gastroesophageal reflux and aspiration lung disease, cystic fibrosis, primary ciliary dyskinesia)
- Evidence for inhaled corticosteroid efficacy is largely lacking for pre-school children

