Diagnosis of Asthma

The diagnosis of asthma can be complex and may be delayed. This is because your asthma symptoms may be different from that of another person and may also be a symptom of another condition for example heart failure.

It is important that you get yourself checked if you get symptoms of asthma so that you can get diagnosed. It’s very important to get a confirmed diagnosis of asthma so that you can get treatment as soon as possible because an asthma that is untreated or undertreated can lead to worsening symptoms and life-threatening asthma.

Diagnosis of asthma will involve your doctor asking you questions about your symptoms, when you get them, if it is triggered by anything, if you have family members who suffer from asthma, if you suffer from allergies and other questions necessary for diagnosis. Although asthma diagnosis is clinical, that is it can be diagnosed in the doctor’s office after history taking and examination, there are some confirmatory test your doctor may ask you to do.

Asthma tests can be used to diagnose and monitor asthma. They can also be used to see how your lungs are responding to asthma medicine(s). These tests are usually only suitable for people who are aged five years and above.

Your doctor will usually wait till test results before prescribing you any medicines for asthma, but your doctor may prescribe you medicines before a confirmed diagnosis of asthma is made if you become unwell with symptoms. If this is the case, your doctor will still need to conduct a test to confirm the asthma diagnosis.

While asthma test remains the best way to the best way to either confirm or rule out asthma, you doctor may do a ‘trial of treatment’. A ‘trial of treatment’ is when the doctor prescribes you asthma medicine(s) to see if you get better with them. Lung function test (breathing test) which is used to measure how well your lungs are working may be used before and after the trial to determine whether or not the asthma medications have made any difference.

If you get better with the medicines, it indicates that you may have asthma.

Your doctor may ask you to reduce or stop the medicine to determine if your symptoms returns. If your symptoms return, then it indicates you may have asthma.

However, if your symptoms do not improve with this trial, your doctor may start looking into other reasons you may be experiencing these symptoms.

Tell your doctor immediately if your asthma gets worse during this trial.

Tests used in the diagnosis of asthma

Peak Flow in the diagnosis of asthma

This is a simple lung function test that measures how quickly you can blow air out of your lungs. It’s commonly used to diagnose and monitor asthma. It can be done in hospital or at your home over a period of time. You may have to keep a peak flow diary for a few weeks.

How is a peak flow test done?

You will be asked to take a full breath in, after which you blow out as fast as you can into a hand-held plastic tube device called a peak flow meter. The measurement that is taken is referred to as your ‘peak flow’ and the units is usually in litres per minute.

How to measure your peak flow

Your doctor or healthcare professional will show you how to take your peak flow measurement at home using your own peak flow meter. Your doctor will usually recommend checking your peak flow in the morning(am) and evening (pm).

Peak flow meter used in diagnosis of asthma
Peak flow meter used in diagnosis of asthma

To take your peak flow measurement, you should:

  • Sit or stand in a comfortable position
  • reset your peak flow meter by pushing back to the first line in the scale which is usually around 60
  • hold the peak flow meter at a horizontal position without blocking the scale
  • breathe in as deeply as you can then open your mouth and seal the mouthpiece with your lips.
  • breathe out through your mouth as fast and as hard as you can
  • take note of your reading
  • Repeat at least three times because the highest of these reading is your peak flow score.

Why is peak flow measured?

It is measured to find out if your airways are narrowed.

Peak flow can be used to regularly monitor your asthma.

Your score can be used to find out if your condition is getting better or worse

It can be used to check if your medicines are working

It can be used to check if you are having an asthma attack.

It can be used to find out what your asthma trigger is. If you measure your peak flow before and after contact with a suspected asthma trigger, you may be able to tell if it actually causes your asthma attacks.

It is important that you know what your personal best reading is as your future peak flow tests can be compared to your personal best reading.

Your peak flow scores

Your peak flow score which is also known as your peak expiratory flow (PEF) shows how well your airways are doing and will be displayed on the side of your peak flow meter. This result is in litres of air breathed out per minute (l/min).

A normal peak flow score depends on your age, height, and whether you are a man or a woman.  Ask your doctor what you should consider a normal score.

In diagnosis of asthma, your doctor would usually compare your results to what is expected for someone of the same gender, height and age.

A significant or big difference between your score and a normal score may suggest you have asthma.

A significant or big difference between your present score and your best score taken at a time when your asthma was well controlled may suggest your asthma is not well controlled or that you are having an asthma attack.

Download a peak flow diary here

Spirometry in the diagnosis of asthma

This is a lung function or breathing test which measures the total amount of air you can breathe out from your lungs in a set time. It is carried out using a device called a spirometer. There are different types of spirometer devices.  It is usually the first test used by your doctor to find out if you are likely to have asthma or not.

spirometry
Pulmonary function Test (spirometry)

How is a spirometry test done?

A soft clip may be placed on your nose to stop air escaping from it. Your doctor will ask you to take a very deep breath and blow out as fast as you can, and for as long as you are able to or until no more air comes out, into a mouthpiece of the ‘spirometer’. You will need to repeat the best for at least 3 times to ensure a reliable result.

Spirometry can be used to find out if your inhaled asthma reliever medicines can open up your airways by reversibility testing. To do this your health care professional will ask you to use your asthma reliever medicine through a spacer. The aim is that the medicines opens up your airways. This is known as bronchodilator reversibility (BDR). You will then be asked to blow into the machine a few times after waiting for between 15-20 minutes. The aim is to check if there is a big difference before and after you took the medicines. If your airways are found to be less narrow after taking the medication, then it is very likely that you have asthma.

Why is a spirometry test done?

It is measured to find out how much your airways were narrowed before and after taking reliever medicines which can help in diagnosis of asthma

It can be used to regularly monitor your asthma.

Your score can be used to find out if your condition is getting better or worse during asthma reviews.

It can be used to check if your medicines are working

It can be used in diagnosing other lung conditions.

What does spirometry measure?

Slow vital capacity or (VC): The amount of air that you can blow out in a relaxed manner.

Forced expiratory volume in one second or (FEV1): This is amount of air you can blow out in one second. Healthy and normal airways will usually be able to blow out most of the air in the lungs.

Forced vital capacity or (FVC): This is the amount of air you can blow out in one complete breath after you have taken a deep breath.

FEV1/FVC: This is ratio of the amount of air you can blew out in the first second (FEV1) to Forced vital capacity or (FVC).

Your spirometry results

Your doctor will usually not be able to give you your results immediately because it has to be seen by a specialist. They will usually look at your result and compare it with someone of the same gender, height and age.

Spirometry will show if your airways are narrowed or restricted. It will not tell you if it is inflamed but a narrowed airway may be due to inflammation.

Think of it as a pipe that is narrow probably due to a blockage. It will take longer for water to pass through the pipe. That is the same way it will take a narrower lung more time to empty the air in it.

A spirometer will record the amount of air you can blow out in one second. Healthy and normal airways will usually be able to blow out most of the air in the lungs (at least 70%) which means that if your airways are narrower than that of someone of the same gender, height, age and ethnic group, your result will be less.

The ratio of the amount of air you blew out in one second (FEV1) to the amount of air you can blow out in one complete breath after you have taken a deep breath (FVC) measures how much your airway is blocked.

The problem with your lungs could either be “obstructive”, “restrictive”, or a combination of both

Obstructive airways disease: This is where you don’t breathe out as quickly as you would usually do because of your narrowed airways even when you can hold normal amount of air in your lungs as seen in asthma or Chronic obstructive airway disease (COPD).

Restrictive lung disease: This is where you breathe in less amount of air because your lungs are not able to fully expand as seen in pulmonary fibrosis.

The reversibility testing shows whether or not your airways have responded to the asthma reliever medicines. A positive response indicates you may have asthma.

Fractional exhaled nitric oxide (FeNO) test in the diagnosis of asthma

This is a simple test that is used to measure how much nitric oxide you breathe out. Nitric oxide is a substance produced in lungs of people with inflamed airways. It is therefore found in high amount in the breath of people with inflamed and sensitive airways which means that a high level of nitric oxide in your breath may suggest that you have inflamed airways. Together with clinical history and other tests, FeNO test can help in confirming the diagnosis of asthma. 

Some factors such as smoking can influence the results of your FeNO test. For this reason, FeNO is usually done in addition with other tests in the diagnosis of asthma.

How is a FeNO test done?

You will be asked to breathe into a cardboard tube attached to a hand-held monitor. The reading will show up on the screen of the monitor.

You will need to breathe in deeply, with your mouth open. You will then be asked to breathe out slowly and steadily into the mouthpiece until your lungs are empty. You may have to do this test a few times to get a reliable result.

Why is FeNO done?

It is measured to find out how much your airways are inflamed which can help in the diagnosis of asthma.

It can be used to regularly monitor your asthma.

Your score can be used to find out if your condition is getting better or worse during asthma reviews.

It can be used to check if your medicines are working

It can be used to find out the type of asthma you have whether allergic or non-allergic. This is because you are more likely to have higher levels of nitric oxide in your breath if you have allergic type asthma.

Your FeNO result

Your result shows how inflamed your airways are.

It can also show if you have allergic or non-allergic asthma.

The results will be in parts per billion (ppb) of nitric oxide in your breath. Your health care professional will also check your symptoms, such as cough, wheeze and shortness of breath.

Adult Reading Suggests
> 51 ppb your airways are inflamed, and medication can improve your symptoms
26–50 ppb grey area – if you have symptoms, medication may help
< 25 ppb It is unlikely that you have inflamed airways.

Table adapted from British lung foundation

Child (<12) Reading Suggests
> 35 ppb your airways are inflamed, and medication can improve your symptoms
21–35 ppb grey area – if you have symptoms, medication may help
< 20 ppb It is unlikely that you have inflamed airways.

Bronchial challenge test (direct challenge test) in the diagnosis of asthma

This is a specialised test that is done to measure changes in your airways after breathing in substances that trigger asthma. Methacholine is the most common substance. Histamine is another substance that can be used.

This test is done to intentionally irritate your airways to see how it will react. You will be asked to do a spirometry test to evaluate how sensitive your airways are.

This test is not usually used for children and recommend for adults seventeen and over.  They are also not used to monitor your asthma.

Your doctor will usually ask you to stop certain medication and inhalers before the day of your test. This is to ensure an accurate result. Do not take caffeine containing products like tea, coffee and chocolate on the day of your test. Some factors like smoking may affect your test.

How is bronchial challenge test done?

You will be asked to inhale a substance (histamine or methacholine) through a hand-held device or a nebuliser. If you have asthma, the substance will cause the airways to become inflamed, narrower and may trigger asthma symptoms. This will cause a drop in lung function which will be detected with breathing tests (spirometry). This breathing test is usually done before and after you take each dose of the test substance to measure the degree of narrowing of your airways. If your airways become inflamed and narrowed or your asthma symptoms are triggered while having the test done, your specialist asthma doctor will be there to monitor and treat you if required. At the end of the test you will be given an inhaled reliever medicine to help open the airways again.

You start the test with a small dose of the substance. If your breathing remains unchanged, you will get a progressively larger dose of the substance until either you have a significant drop in lung function, or you reach a maximum dose with an unchanged lung function.

How bronchial challenge test is done

1.  A spirometry test is done to ascertain what your baseline lung function is. Provided your lung function is not too low, the test will continue.

2. Test using a very low dose of test substance. Repeat the spirometry test immediately after inhaling the test substance and again a few minutes after.

3. Inhale higher dose of test substances than the previous dose provided your lung function remains unchanged after the lowest used dose of test substance. Repeat the spirometry test immediately after inhaling the test substance and again a few minutes after.

4. You will be given higher dose of test substances than the previous dose provided your lung function remains unchanged after the previous dose of test substance followed by spirometry testing.

5. The test is considered complete after you have a significant drop in lung function with a drop in forced expiratory volume at 1 second (FEV1) of 20% or more, or you reach a maximum dose with an unchanged lung function. You will then be given an inhaled reliever medicine to help open the airways again. A spirometry test will be done at the end to ensure your lungs are back to normal before being allowed to go home.

Why is bronchial challenge test done?

It is done to find out how your airways reacts to triggers

It may be used if other tests do not conclusively confirm that you have asthma.

Your bronchial challenge results

A bronchial challenge test will be said to be positive if the test substance causes your lung function (FEV1) to drop by 20% or more compared to your baseline. For a positive result, concentration of the test substance given at the point your lung function drops by at least 20% is your test result.  A positive test will make your doctor consider a diagnosis of asthma. It will be said to be negative if you do not have a drop in lung function and the last dose given will be your result. A negative result nearly rules out a diagnosis of asthma.

Allergy tests

The two main types of allergy tests people who have asthma might have are skin prick or blood test.

Allergy tests are not usually used to diagnose asthma but if the tests confirm you have allergy then it may suggest you are more likely to have asthma.

Allergy tests are commonly used after a confirmed diagnosis of asthma is made to determine the allergen that may be triggering your asthma symptoms. 

Allergens are substances that may cause an allergic reaction.

How are allergy tests done?

How is blood test done?

A sample of blood blood will be taken and tested for the level of specific antibodies (immunoglobulin E antibody) produced by your immune system in response to an allergen.

How is skin prick test done?

Your doctor will usually tell you to stop taking anti-histamine medication a few days before your test

skin prick test
skin prick test

The skin prick test is usually done on the inside of your forearm.

The specialist health care professional doing the test will identify possible allergens that may be causing your allergy. This could be just a few or as many as 25.

A specialist will then mark your arm with a waterproof pen. This is done to help him/her easily identify which allergen is which.

The skin next to the marks will be pricked with tiny amounts of the allergen.

 If you are allergic to any of the allergens used, your skin may become red, itchy, swollen (raised bumps like nettle stings).

Your result should be ready within about 20 minutes.

Your allergy test results

Blood tests are used to find out the amount of IgE antibodies produced in your blood by your immune system in response to a suspected allergen. It will show if your allergy is due to a specific allergen or different allergens.

The skin prick test result will tell you exactly what you are allergic to.  

Share this