How are respiratory tract infections diagnosed?

A stethoscope

A stethoscope is used to listen to your breathing and heart beat. Image: Seregam /

Your doctor will ask questions about your health and any recent illnesses you have had (e.g. a cold or flu), what your symptoms are, what medicines you are taking, details of your medical history, and if you have any other medical conditions (e.g. asthma).

The doctor may listen to your chest using a stethoscope to listen to your breathing and heart beat, and they may examine your ears using an otoscope (a medical device with a small light on the end that is used to look inside the ears).

Diagnostic tests


Most respiratory tract infections (RTIs) can be diagnosed based on your symptoms and a physical examination by your doctor without the need for an X-ray.

However, if your doctor thinks you have pneumonia, you will probably need a chest X-ray to confirm the diagnosis.

X-rays are not generally used to diagnose a sinus infection (sinusitis) because an X-ray is usually not helpful in confirming the diagnosis.

Computerised tomography (CT) scans

Computerised Tomography (CT) scans are not normally needed to diagnose respiratory tract infections.

CT scans may occasionally be used for sinus-like symptoms, only if a specialist considers it is necessary to diagnose your illness. This is because the CT scan involves a large dose of radiation, and there is the risk that this may affect the lens of the eye.

An otoscope

An otoscope is used to look inside the ear. Image: Cameron Swinton /

You may have a CT scan if you:

  • have severe symptoms that are not typical of an RTI
  • only have symptoms on one side of your head
  • have already been prescribed antibiotics for an initial suspected sinus infection
  • there is blood in the mucus or liquid in your nose
  • the pain in your head or face is severe
  • the position of one of your eyes is affected.

Laboratory tests

Laboratory (pathology) tests can sometimes be used to diagnose an RTI. For example, a test can show if bacteria are causing your infection, and if so, which antibiotic might help. This usually means taking a sample from the affected area. However they are not often used for common RTIs. A doctor can often diagnose your condition without a test, and the test may not make a difference to your treatment anyway.

Laboratory tests will usually only be used when it is important to find out exactly what is causing the infection (e.g. whooping cough), so that you can get the right treatment.

Sputum (spit or mucus): your doctor may take a sample of the sputum or mucus that you cough up. This will be sent to a laboratory and used to identify what is causing your infection.

Nasal or throat swab: your doctor may take a sample of cells and mucus from inside your nose, throat or tonsils using a sterile cotton swab (a long cotton bud). This is usually painless and will help to find out what is causing your infection. Swabs can test for both viral and bacterial infections.

Urine: a urine sample is also occasionally used to help identify specific bacterial infections (e.g. caused by Streptococcus pneumoniae or Legionella pneumophila).

  • Respiratory Expert Group. Therapeutic guidelines: Respiratory; Pneumonia, Sinusitis, Influenza. Melbourne: Therapeutic Guidelines Ltd; March 2012. (Accessed 21 March 2012).