The diagnosis of asthma

A diagnosis of asthma is made after a number of things
  • A detailed and careful history
  • Physical examination
  • Lung function tests
  • Peak Flow diary
  • Reversibility testing
  • In some cases a chest x-ray to exclude other causes for symptoms

Detailed History

You doctor will ask you many questions about your symptoms, type, severity, things that make it better worse. Other important factors include family history, allergies, pets, occupation, smoking history, eczema, hayfever and your health in general

Physical Examination

The doctor will assess your lung expansion, shape of lungs, listen to the air entry in and out of your lungs and may tap with his fingers over the lung zones.

Assessing Lung Function

Peak flow meter

  • The peak flow meter is a small device which measures the maximum flow of air that can be breathed out. It is a good simple measure of how much the airways are narrowed in asthma and how well a persons asthma is being controlled.
  • Peak flow readings are compared with a standardised set of readings based on a persons, age, sex and height.. However, for some asthmatics readings are compared to their personal best reading ever recorded.
  • Low readings can be suggestive of limited air flow and often your doctor will ask you to take 3 readings first thing in the morning and 3 readings in the evening and record them over a period of a couple of weeks.
  • For some patients they use a peak flow meter daily and their readings to help them monitor their asthma.
  • For infections, exacerbations and attacks the device can be used anytime to assess lung function..
  • Patients soon learn what is a good and bad reading for them and according to the measured value, medication may need to be started, or increased and further advice sort from their GP.
  • Teaching patients how to perform peak flow readings and self monitoring allows them to feel confident with their medication and importantly to act quickly when coughs, colds and acute exacerbations present.
  • Peak flow meters are available on NHS prescription.

How to measure your peak flow

  • Peak flow is measured as per litres per minute
  • You always take 3 readings and record the best score.
  • Always stand when taking your peak flow.
  • Hold the meter horizontally and with your fingers out of the way of the slider cursor.
  • Slide the cursor to the bottom of the graduated scale to zero.
  • Take a deep breath in to the maximum of your lung capacity, with your mouth open.
  • Close your lips firmly around the mouthpiece and blow as hard and as quickly as possible.

Many undiagnosed asthmatics put their breathing symptoms down to being unfit or part of ageing. Serial peak flow readings through keeping a diary of symptoms and reading and or a reversibility test help confirm a diagnosis.

Reversibility Testing

This is a quick test that can be performed in the asthma clinic at your GP surgery. The best of 3 peak flow readings are taken, then a beta 2 agonist inhaler such as Salbutamol is given and 15 to 20 mins later 3 more peak flow readings are taken. If there is a variation of 15% or more then a diagnosis of asthma is made.

The variation of 15% is not a complete cut off and asthma is strongly suspected with a variation of 10%, as a reversibility test is only part of the process in making an asthma diagnosis


Other Lung function tests

Spirometry is widely used to assess and investigate many lung disorders including asthma. It is accurate and measuring lung volume and distinguishing between diseases that involve narrowing of the airways such as asthma and diseases where there is loss of lung capacity.

Spirometry is provides objective information and is the gold standard for testing lung function.

Making a diagnosis in Children

Under the age of 5 it is more difficult to make a diagnosis as the objective tests we perform on adults are more difficult to carry out on young children. Children also have many episodes of coughs, colds and wheezy chests, which are not always asthma related. It is therefore important that a good history of symptoms is obtained, afamily history and that children are closely monitored and that a referral to a paediatrician be made if there are any concerns.

Chest X-ray

Where there are symptoms of persistent cough, recurrent infections, a person that smokes or any uncertainty over a diagnosis a chest x-ray is an important investigation.

Most asthmatic patients have a normal chest x-ray .

A normal X-ray result can sometimes discourage an asthmatic person to follow their treatment plan because they believe that a normal X-ray result is tantamount to saying they do not have asthma.

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