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.