Health A-Z

Medical Content Created by the Faculty of the
Harvard Medical School

Asthma

Diagnosis

Your doctor will ask about:

• Any symptoms you have

• How severe they are

• When and where they occur

• How frequently they occur

• What triggers and relieves them

These details will help your doctor find ways to help prevent your asthma attacks.

Your doctor also will want to know about:

• Your personal history of allergies and respiratory illnesses

• Your family history of asthma, allergies and respiratory illnesses

Your doctor will listen to your back with a stethoscope to detect wheezing.

During an attack, your doctor can assess the severity of your flare-up. He will listen for the amount of airflow in your lungs. He will also observe how you are using your chest muscles to breathe. Blue lips or skin are a sign that you are not getting enough oxygen.

Other tests may be done in the office. These include measuring the speed of the air you can exhale forcibly. This is done with a device called a peak-flow meter.

Another test, called pulse oximetry, measures oxygen levels in your blood. It is done by placing a small plastic clip on the tip of your finger.

During an asthma flare-up, blood tests may be done to check for infection. An arterial blood gas (ABG) test can be done on a blood sample. It provides a more accurate measure of oxygen levels. Your doctor also may want you to have a chest X-ray.

Two tests are commonly used to show how well your lungs are functioning:

• Spirometry — This is a more thorough test. It is used to confirm an asthma diagnosis. It also provides more details about your lung function.

During spirometry, you exhale into a device that analyzes the amount and volume of airflow. One part of the test may be repeated after you are given a bronchodilator. This medication relaxes the muscles surrounding the airways. If airflow improves with a bronchodilator, it indicates that you have asthma.

Sometimes a challenge test is done when spirometry appears normal. For this test, you inhale a medication to see if it causes your airway muscles to tighten up. People with asthma are more sensitive to this medication: their airway muscles are more likely to tighten up.

• Peak-flow meter — This is a small portable tube. It provides a quick and easy measurement of air flow from the lungs. It measures the speed of air expelled when you blow forcibly through it.

Peak-flow meters often are given to asthma patients for use at home. They can use them to monitor their asthma. These devices help to detect the earliest signs of an asthma flare-up.

Your doctor may want to do a blood test or allergy skin testing. These tests are used to determine specific substances ("allergens") that can trigger an allergy.