http://www.nhlbi.nih.gov/health/dci/Diseases/Asthma/Asthma_Diagnosis.html

Medical history:  Doctor will ask about a family history of asthma or allergies, as well as one�s own personal asthma symptoms (how often do they occur?  Specific time of the day or night? What triggers the symptoms?)

Physical examination: doctor will listen to one�s breathing as well as look for other physical symptoms of asthma and/or allergies, such as wheezing, runny nose or inflammation of the nasal passage, or eczema.

Tests: spirometry � this tests lung function; how much air one can breathe in and our of their lungs, as well as how fast one can breathe out.  Additional testing may include: allergy test, airway sensitivity test, chest X-ray, and determining if it�s actually a disease with the same symptoms of asthma.