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Diagnosis of Asthma

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To make the diagnosis of asthma, the following is required:

Clinical history. Taking into account the symptoms, family and personal history.

Complete physical examination.

Lung function tests, among which are forced spirometry with a bronchodilator test, it is the test that confirms the diagnosis.

Tests used to diagnose 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.

Forced spirometry

It is the test of choice to diagnose and control patients with asthma. It is a reliable, simple, economic test that provides immediate information on lung function. It consists of inhaling deeply until the lungs are filled and blow rapidly through a tube connected to a spirometer until the chest is empty of air. This test is essential in order to evaluate the degree of obstruction of the airways, and measures the lung capacity (forced vital capacity, FVC), and the volume of air expelled in the first second (maximum expiratory volume in the first second, FEV1). When a patient has obstructed bronchi, the air takes a longer time to come out than when they are not. The values that the spirometry measures are compared with the reference values of a normal general population, taking into account the gender, age, height, and weight.

To evaluate if the obstruction of the bronchi is reversible, the bronchodilator test is performed. This consists of repeating the spirometry after the administration of a rapid-acting bronchodilator drug. The bronchodilator test is positive if there is a substantial improvement in the bronchial obstruction parameters, that is to say, that the bronchi are significantly dilated. In this way, and together with the clinical history of the patient, the diagnosis of asthma can be made and carry out follow-up visits after starting the medication.