These four categories are adapted from the NIH (National Institue of Health) guidelines and are used to describe the severity of an individual's asthma.

Mild Intermittent Asthmatics:

• A pulmonary function test greater than or equal to 80% of normal
• Daytime symptoms 2 times a week or less
• Nighttime symptoms 2 times a month or less
• Asthma episodes are brief and the patient is normal in between

Mild Persistent Asthmatics:

• A pulmonary function test greater than or equal to 80% of normal
• Daytime symptoms greater than 2 times a week, but less than once a day
• Nighttime symptoms greater than 2 times a month
• Asthma episodes may affect activity

Moderate Persistent Asthmatics:

• A pulmonary function test greater than or equal to 60%, but less than 80% of normal
• Daily symptoms greater than 2 times a week, and which may last days. Use daily of a quick relief inhaler (reliever inhaler)
• Asthma episodes affect activity
• Nighttime symptoms more frequent than once a week

Severe Persistent Asthmatics:

• A pulmonary function test of less than or equal to 60% of normal.
• Continual asthma symptoms
• Limited physical activity
• Frequent asthma episodes
• Frequent nighttime symptoms