Tests Used to Diagnose Asthma

• Pulmonary function tests (PFTs) are used to test lung performance, but in children younger than 5 years, the results are typically not reliable.
  
  
  • An asthma specialist, such as a pulmonologist or allergist, can perform breathing tests using a spirometer, a machine that measures the amount of air that flows in and out of the lungs. It can detect blockage if the airflow is lower than normal, and it can also detect if the airway obstruction is involving only small airways or larger airways too. The doctor may take a spirometer reading, give the child an inhaled medication that opens the airways (bronchodilator therapy), and then take another reading to see if breathing improves with medication. If medication reverses airway obstruction (blockage), as indicated by improved airflow, then there's a strong possibility that the child has asthma. A peak flow meter is a simple device used to measure the peak flow of air coming out of the lungs when a child is asked to blow air into it. The peak flow meter readings are different than spirometer readings. However, a child can have a normal peak airflow and still have airway obstruction that is not detected with spirometry. The peak flow can have a normal value while the values for other parameters, such as forced expiratory volume in 1 second (FEV1) or forced expiratory flow during mid-portion of forced vital capacity (FEF25-75), are reduced suggesting airway obstruction. Thus, spirometry is more informative compared to only peak flow meter readings.
    
    
  • Another test is called plethysmography. This test measures lung capacity and lung volumes (the amount of air the lung can hold). Patients with chronic persistent asthma may have lungs that are over-inflated; over-inflation is diagnosed when a patient has increased lung capacity detected by this test.
  
  
• Other tests called bronchial provocation tests are performed only in specialized laboratories by specially trained personnel. These tests involve exposing patients to irritating substances and measuring the effect on lung function.
  
  
• Patients with a history of exercise-induced symptoms (eg, cough, wheeze, chest tightness, pain) can undergo an exercise challenge test. This test is usually done in children older than 6 years. The baseline (or usual) lung function for the child is measured (using spirometry) while the child is sitting still. Then the child exercises, usually by riding a stationary bicycle or walking fast on a treadmill. When the child's heart is beating faster from the exercise, the lung function is measured again. Measurements are taken immediately after the exercise and at 3, 5, 10, 15, and 20 minutes after the first measurement. This test detects decreased lung function caused by exercise. 
  
  
• Your doctor may take a chest x-ray (radiograph) if the asthma isn't helped by the usual treatments.
  
  
• Allergy testing can be used to identify factors your child is allergic to because these factors might contribute to asthma. Once identified, environmental factors (eg, dust mites, cockroaches, molds, animal dander) and outdoor factors (eg, pollen, grass, trees, molds) may be controlled or avoided to reduce asthma symptoms.
  
  
• Ask your doctor for more information on these and other tests.