There are several ways to diagnose pneumococcal infections, and the tests you have will depend on your symptoms.

Physical examination

If a pneumococcal infection is suspected, your GP will listen to your chest with a stethoscope. The fluids produced during an invasive pneumococcal infection often cause a distinctive crackling sound.

Blood test

You may have a blood test to check for the presence of bacteria. A high number of infection-fighting white blood cells may indicate the presence of an infection. The blood sample can be sent to a laboratory so the bacteria that caused the infection can be identified.

Radiography

Several different types of imaging tests may be used, depending on your symptoms.

X-rays may be able to highlight the presence of fluid in the lungs, which would indicate a lung infection. An X-ray uses radiation to produce images of the inside of the body.

Other imaging tests that may be used to investigate a potential pneumococcal infection include:

• a computerised tomography (CT) scan
• a magnetic resonance imaging (MRI) scan

Blood pressure test

Your blood pressure may be measured, as a serious infection can often lead to a decrease in blood pressure. 

Lumbar puncture test

A lumbar puncture test involves taking a sample of cerebrospinal fluid (the fluid that surrounds the brain and spine) from the base of your spine and checking it for the presence of bacteria. A local anaesthetic will be used to numb the area. If the sample contains infection-fighting white blood cells and/or bacteria, it may indicate that you have meningitis.

Urinary antigen test

A urinary antigen test is a relatively new type of test used to help diagnose a pneumococcal infection.

It involves taking a urine sample, then carrying out a technique known as an immunochromatographic assay. This can detect the distinctive protein molecules that make up the outer shell of the S. pneumoniae bacteria.