Is this consistent with asthma?

[rickyg]

I recently had breathing tests to check for asthma that showed only a 5% increase of lung function after using the inhaler.  Is this consistent with asthma, or would this be considered normal?  I had thought that the difference before the inhaler and after would show more of an increase if indeed it was asthma.  My doctor had said if a person isn't having symptoms at the time of the test, it would come out normal.  But isn't the reason for the test in the first place to show lung function consistent with asthma even if you are feeling fine at the moment?  I know people who have asthma - some severe and some very mild - and all of them has said that they were symptom-free at the time of their testing, yet the results clearly showed they had asthma, and their lung functions showed a marked improvement after using the inhaler, even though they were breathing fine before.  
Is there a span of percentages that are used to determine if it's asthma - or isn't?  I just think a 5% improvement would be a normal response.  

Thank-you for you help.

[National Jewish]

You have asked some difficult and excellent questions regarding interpretation of lung function and the diagnosis of asthma. A 5% improvement after a bronchodilator does not make the diagnosis of asthma at all. However, it does not rule out the diagnosis either. It is possible that someone with asthma is doing very well at the time of testing and his or her response cannot go beyond the normal range. This can happen with people who have fairly mild asthma and their lungs are normal a good part of the time. If you feel you have asthma, the test can be repeated when you feel you are having a problem. At that time, it should be easy to determine if you have reversibility consistent with asthma.