Once an accurate diagnosis of asthma has been found, and differential diagnoses have been excluded, severity of the disease can be assessed using the dose of treatment and level of disease control. A patient receiving high dose inhaled corticosteroids with additional controller medication, who continues to experience exacerbations and requires short courses of oral corticosteroids, has severe asthma. A patient is also considered to have severe asthma if they are controlled on high dose inhaled corticosteroids with other controllers, but step down the dose of inhaled corticosteroids without experiencing deterioration in disease control.

Patients with severe asthma that remains uncontrolled despite high doses of controller medications, may benefit from further investigations and a tailored treatment plan to achieve ultimate asthma control. This type of treatment often requires consultation with a specialist.