The best time to check for allergens in allergic asthma is still during an asthma attack. At this time, due to the body's strong immune response to external allergens, also referred to as a hypersensitive reaction, checking for allergens can likely yield some positive results.

However, there are many methods for screening allergens, such as drawing blood to check for IgE antibodies, or using skin prick tests to assess reactions to different allergens. However, if it is during the acute phase of an asthma attack, it is recommended to use the blood drawing method, which is relatively safer. Using skin prick tests might exacerbate the patient's allergic reaction, and may even lead to an acute asthma attack, or severe asthmatic conditions.

Therefore, there are significant considerations to be made when choosing different methods for allergen testing.