What diagnostic testing is used to diagnose asthma?

The most helpful diagnostic tests for suspected asthma
are pulmonary function tests, often referred to as PFTs
 and the single most important
PFT, both for asthma diagnosis and for follow-up, is
spirometry.Other useful medical tests include blood tests
and X-ray studies. Additional, more specialized studies
may be obtained depending on the clinical picture.

 An example of a specialized study is skin-prick testing for
suspected allergy. Blood tests are valuable in getting an
overall picture of a person’s health, as well as in excluding
other diagnoses. Assessment of immune function and
allergies, for example, can be performed in part via blood
testing. X-ray studies include conventional chest X-rays,
as well as three-dimensional chest CT (computerized
tomography) scans. Chest X-rays and CT scans provide
information about the anatomy or structure of the lungs
and larger breathing passages. In quiescent, controlled
asthma, the chest X-ray should be entirely normal. The
same is true of the chest CT scan. During an exacerbation,
however, the lungs’ appearance on an X-ray may
suggest what radiologists call hyperinflation, and the CT
might reveal air-trapping. Both findings reflect the uneven
lung filling and emptying when breathing occurs through
inflamed, constricted air tubes.
Magnetic resonance imaging, scanning, and positron
emission tomography scanning, while useful in other
types of lung diseases, are not required in diagnosing
asthma. The same is true of nuclear medicine scans,
such as ventilation-perfusion scans and gallium scans.