Chest infection, adult - Diagnosis 

Diagnosing adult chest infection 

Your GP can usually diagnose acute bronchitis and pneumonia.

A medical diagnosis of acute bronchitis is not usually needed, unless your symptoms are particularly severe or last longer than three weeks.

Acute bronchitis

Acute bronchitis is usually a mild illness that goes away on its own, so there is usually no need to see a GP.

If you do see your GP, they will usually be able to make a diagnosis by asking about your symptoms and listening to your chest using a stethoscope (a piece of medical equipment that is used to listen to the heart and lungs).

Ruling out other conditions

In confirming a diagnosis of acute bronchitis, your GP may need to rule out other lung infections, such as pneumonia, which has similar symptoms to bronchitis.

If your GP thinks that you may have pneumonia, you will probably need to have a chest X-ray. They may also take a sample of mucus for testing.

If an undiagnosed underlying condition is suspected, such as asthma or emphysema (damage to the small airways in your lungs), your GP may suggest that you have a pulmonary function test.

If you have a pulmonary function test, your GP will ask you to take a deep breath before blowing into a device called a spirometer, which measures the volume of air in your lungs. A decreased lung capacity may indicate that you have an underlying health problem.


If you suspect that you have pneumonia, you should see a GP.

To help make a diagnosis, your GP will ask you about your symptoms. For example, they may ask you:

  • whether you are breathing faster than usual (respiratory rate)
  • whether you feel breathless
  • how long you have had your cough
  • whether you are coughing up phlegm (thick mucus) and what colour it is
  • whether the pain in your chest is worse when you breathe in or out

Your GP will probably use a stethoscope to listen to the back and front of your chest to check for any crackling or rattling sounds. They may also tap your chest and listen to the sound that is produced. If your lungs are filled with fluid, they will produce a different sound compared with normal, healthy lungs.

Your blood pressure will also be checked because an unusually low blood pressure (hypotension) may be a sign that you have a more serious type of pneumonia.

Your GP may also carry out a test called a pulse oximetry test. This test is used to measure how much oxygen your lungs are able to breathe in. A sensor is put on your fingertip, ear or toe. The sensor sends out light waves and a computer that is connected to the sensor measures how the light waves are being absorbed.

Oxygen can affect how the light waves are being absorbed. Therefore, by analysing the results, the computer can quickly determine how much oxygen is present in your blood. Unusually low levels of oxygen may be a sign that you have a more serious type of pneumonia.

Further testing

Further testing is usually only needed if your chest infection symptoms are severe. A chest X-ray can highlight the extent to which pneumonia has affected your lungs. Other tests that your GP may suggest include:

  • sputum test, where you cough up some phlegm (mucus) into a container so that it can be tested in a laboratory
  • blood tests

The samples that are taken during sputum and blood tests will be analysed in a laboratory to help identify the germ that is causing your infection.

So that treatment is not delayed until the test results are back, your GP will usually begin treatment with broad-spectrum antibiotics, which are known to be effective against a wide range of bacteria.

Once the germ that is causing your infection has been identified, your GP may adjust your treatment accordingly. 

Page last reviewed: 14/05/2012

Next review due: 14/05/2014


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Screening for lung cancer

Although uncommon, pneumonia can sometimes be a symptom of underlying lung cancer in people who smoke and are 50 years of age or over.

If you smoke, have pneumonia and are 50 or over, your GP may refer you for a chest X-ray. Lung cancer usually shows up on X-rays as a ‘white-grey’ mass.

If the first X-ray does not detect cancer, a second, follow-up X-ray is recommended six weeks later. This is a way of ‘double-checking’ that all is well with your lungs.

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