Asthma – Diagnostic Tests Explained

Spirometry

Spirometry is a simple and quick test that that helps doctors see how well the lungs are working. It doesn’t require much preparation.

Before the Test

• On the day of the test, you may need to stop taking certain medications.
• Try not to smoke, or not eat a huge meal right before the test.
• No need to fast or follow a special diet.

During the Test

• Sit upright in a chair
• A small clip goes on your nose to make sure you breathe only through your mouth.
• You will then put a mouthpiece in your mouth, which is connected to the spirometer.
• The doctor will guide your breathing. It usually starts with normal breaths, followed by a deep breath in and fast exhales.
• The spirometer records how how much air you can blow out and how fast you can do it.  

Why Spirometry is Important

• To diagnose asthma.
• To determine how severe your asthma is.
• To monitor how well treatment is working. 

What Spirometry Measures

• Forced Vital Capacity (FVC): The total amount of air you can breathe out after a deep breath 
• Forced Expiratory Volume in 1 Second (FEV1): The amount of air you can breathe out in the first second of exhaling 
• FEV1/FVC: The amount of air you breathed out in the first second compared to the total amount of air you can breathe out 
• Peak Expiratory Flow (PEF): The fastest speed you can blow air out. This can be measured with a spirometer or a handheld peak flow meter which is also available for home use 

Watch How Spirometry is Done

• Video 1
• Video 2

Allergy Testing

Doctors use different tests to find out if allergies are causing or making asthma symptoms worse. The main types of allergy testing are skin tests, challenge tests, and blood tests.

Skin Test (Prick Test)

This is the most common type of allergy test.

• A small needle gently scratches the skin, usually on the forearm or back
• A tiny amount of a possible allergen is placed under the surface of the skin
• If the body reacts to the allergen, the skin may become red, itchy, or slightly swollen where it was pricked.
• Most allergic reactions appear within the first 15 mins. 
• Before the test: Your medical team may advise stopping certain medications, hard exercise, smoking, or caffeine before the tests. These things can all affect the results.  
• Video explaining skin tests 

Challenge Test

This test involves the exposure to a possible allergen in a controlled medical setting.

• You will inhale, swallow, or get the allergen placed on your skin. 
• You will then be observed for signs of an allergic reaction 

Before the Test

• Check with your medical team about stopping any medications – such as antihistamines, that could affect the results. 

Blood Test

This test checks for signs on an allergic reaction inside your body.

• A small sample of blood is taken and sent to a lab.
• The lab measures a substance called immunoglobulin E (IgE), which is linked to allergic reactions.

What the test shows

• Total IgE: the total amount of IgE antibodies in your blood.
• Specific IgE: IgE levels related to a specific allergen.

People with allergy-related asthma often have higher IgE levels. These levels can rise depending on how severe the asthma is.

Bronchoprovocation Testing 

Bronchoprovocation tests check how “responsive” your lungs are. These tests help doctors see whether your lungs react normally or show signs of being overly sensitive (hyperactive). They also measure how strong that reaction is.

Before the test

Doctors may ask you to stop taking any antihistamines or products with caffeine (e.g., coffee, tea, chocolate), stop smoking, and heavy exercise. These can affect results. 

Types of Testing

Indirect Test

Indirect bronchoprovocation tests don’t use allergens. Instead, they trigger the airways in other ways to check for narrowing and signs of a hyperactive response. 

• Common methods include exercise, mannitol, or hyperventilation.
• These methods don’t directly act on airway muscle cells. Instead, they lead to the release of mediators, which then affect the airway muscles. 
• These mediators can trigger inflammation and cause the airways to narrow- a sign of hyperresponsiveness. 

Direct Test

Direct bronchoprovocation tests use substances like metacholine or histamine that directly affect airway muscle cells. 

• The test begins with a spirometry to measure your lung function before any exposure.
• After this, you will inhale a small amount of the testing substance.
• The amount will slowly be increased, while the reaction of the airways is measured through repeated spirometry tests. 
• This helps to determine how much narrowing, or bronchoconstriction, occurs in response. 
• At the end of the test is over, you will get medication to help reopen the airways and make breathing easier again. 
• Test results: If the spirometry reading drops by more than 20% from the starting value, the test is considered positive. This shows that the lungs are hyperactive – a common sign in asthma. 
• Video explaining bronchoprovocation tests

Exhaled Nitric Oxide

An exhaled nitric oxide test measures inflammation in the airways. Inflammation can cause swelling and narrowing, which are common in asthma.

• During the test, you will need to take a deep breath in, followed by a slow exhale into a tube. 
• The tube is connected to a computer that measures the amount of nitric oxide in the breath.
• The doctor or technician may ask you to repeat breathing in and out several times to ensure an accurate result.
• The test is short and usually takes no longer than 15 minutes.
• Results: In asthma, nitric oxide levels are often higher than normal because inflamed airways produce more nitric oxide. 

Peak Flow Meter

What is a Peak Flow Meter and What Does it Do

• Is a small, hand-held tool
• Quickly measures how fast you can exhale after a deep breath
• Is often used to track changes in asthma and can help detect worsening symptoms early

How to Use a Pick Flow Meter

• Take a deep breath in and then blow into the mouthpiece as hard and fast as possible
• It is important to sit or stand upright during the test
• Should be done 3 times, and the highest reading recorded as the daily peak flow
• Results vary based on various factors (e.g., age, height, sex)
• Daily monitoring can include: 
  • Writing down the peak flow result (phone or asthma journal)
  • Noting the use of any immediate-relief inhalers or medication
  • Recording any asthma symptoms

Since different models of peak flow meters exist, it’s important to learn proper technique from your medical team to ensure reliable results.