On July 1, 2009, the American Thoracic Society and the European respiratory Society published guidelines on the assessment of asthma control, asthma severity, and asthma exacerbations. I searched both of their websites for the guidelines, however the guideline is not available on either yet. A good summary appears onthis news website. I agree with the definitions in the article. I recommend each patient with asthma and their care providers get very familar with the definitions. They should be used whenever refering to their asthma.
I try to use them in my assessments and I will try to use them verbally during my patients' office visits. (Paraphrased from the article above...) Asthma control: signs and symptoms of active asthma, such as symptom-free days, reliever use, lung function, quality of life, a daily diary (preferably electronic) and a record of visits to doctors and the emergency room; Asthma severity: the intensity of treatment required to achieve good asthma control; Asthma exacerbations: as events where symptoms worsen enough to require a change in treatment.