Diagnosis of Asthma

Forced spirometry with a bronchodilator test. This test is essential for the diagnosis and follow-up of asthma. It measures the amount and velocity of the expired air during exhalation. One of the parameters used to quantify the obstruction of the airways is the volume of air exhaled in the first second (FEV1). It is a basic test to measure these flows. Afterwards, a bronchodilator is administered and the test is repeated. The results show the reversibility of the obstruction which is characteristic of patients with asthma. Although the results may be normal, this test does not exclude the diagnosis of asthma, and more diagnostic tests must be performed.

Peak expiratory flow (PEF) monitoring. It is a test that the patient can perform at home, and it measures the maximum velocity of the air that is exhaled. It serves for the diagnosis as well as for the control of the disease, being able to detect an early deterioration or the response to treatment.

Bronchial challenge test. It is performed by the controlled inhaling of a substance (methacholine or histamine) that produces this obstruction of the bronchi. A series of spirometries are perform to observe the gradual decrease of the FEV1, demonstrating the bronchial hyperresponsiveness.

Fraction of exhaled nitric oxide (FeNO). It measures the amount of exhaled nitric oxide, which indirectly shows the level of inflammation in the airways.

Chest X-Ray. The chest x-ray is usually normal in asthmatic patients. It is used to rule out complications and other diseases with similar symptoms, such as aspiration of a foreign body, respiratory infections, and bronchial malformations.

Allergy skin tests (prick test). It is used to detect respiratory allergies. It is carried out on the front of the forearm. A drop of the most common pneumo-allergens is placed in contact with the skin, using the prick test technique, and the skin reactions that are produced are measured.