There are several different tests used to diagnose and monitor asthma. Below are the most common tests ordered, along with why and how they’re done, and what the results indicate.

Lung Function Test (Spirometry)

  • Measures the amount (volume) and/or speed (flow) of air that can be inhaled and exhaled in the lungs
  • In this test, the patient performs several hard breaths into a machine.
  • Results are measured by the patient’s ability to breathe properly.
  • This test is very difficult to perform in children.

Methacholine Challenge Test

  • Tests a patient's reaction to methacholine, a known asthma trigger.
  • Patient is given a device to breathe in the methacholine.
  • Any spasm or narrowing of the airway can indicate asthma.

Chest X-Ray

  • Rules out any other cause of blockage/narrowing of the bronchi from infection to fracture
  • This is a non-invasive test. A picture is taken of the chest and lungs.
  • Asthma cannot be detected through x-ray, but other abnormal conditions of the lung, chest and/or heart can be.

Strip Test

  • Tests the pH of the digestive system to rule out gastroesophageal reflux disease (GERD) or heartburn
  • The procedure is done with a thin, plastic tube with a sensor that measures the amount of acid backing up into the esophagus.

CT Scan of the Sinus

  • Looks at the inflammatory conditions and fluid levels in the sinus
  • This noninvasive medical test takes a picture of the bones, soft tissues and blood vessels.
  • A clear sinus rules out sinusitis.

Blood Test

  • Tests for levels of immunoglobulin IgE and eosinophils, which are antibodies
  • If asthma is due to an allergy, the level of these antibodies will be raised.