Diagnosing disorders of consciousness 

It takes extensive testing to assess levels of wakefulness and awareness before a disorder of consciousness can be confirmed.

This may involve tests such as brain scans, but is largely based on the specific features a person displays, such as whether they can respond to commands.

Read more about the features of disorders of consciousness.

The Glasgow Coma Scale

Doctors can score a person's level of consciousness using a tool called the Glasgow Coma Scale. This assesses three things:

  • eye opening – a score of 1 means the eyes don't open at all, and 4 means opens eyes spontaneously
  • verbal response to a command – 1 means no response, and 5 means a person is alert and talking
  • voluntary movements in response to a command – 1 means no response, and 6 means a person can follow commands

A lower score indicates a more severely impaired consciousness, such as a coma, although this level will be monitored regularly to look for any changes.

The brain injury association Headway has more detailed information about the Glasgow Coma Scale.

Brain scans

Brain scans are used to help assess the level of brain damage in someone with impaired consciousness, but can also be helpful in assessing how a person responds to stimulation. This can be especially useful if a person cannot move or speak.

There are several types of scans that can assess brain function, but most commonly a magnetic resonance imaging (MRI) scan is used. An MRI scan uses strong magnets and radio waves to create a detailed image of the brain.

Brain scans can show changes if the brain is responding to lights and sound. However, they do not necessarily show awareness because the brain is able to respond to stimulation even without you being aware of it.

Research is being carried out into ways brain scans can be used to show true awareness.

Criteria for a vegetative state

A vegetative state is when a person is awake but showing no signs of awareness. Doctors are particularly careful when diagnosing a permanent vegetative state, as there is a risk of misdiagnosis.

A confident diagnosis can only be made if the following criteria have been met:

  • the cause of the brain injury has been established – for example, if a case of meningitis is suspected, a diagnosis can be confirmed by testing the fluid that surrounds the brain for infection
  • it has been confirmed that drugs or medication are not responsible for the symptoms
  • it has been confirmed that treatable problems with the body's chemistry (a metabolic disorder) are not responsible for the symptoms of loss of awareness – an example of a metabolic disorder is a diabetic coma, where people lose consciousness because their blood sugar levels are either dangerously high or dangerously low
  • the possibility of a treatable cause in the brain, such as a brain tumour, has been ruled out by brain imaging scans, such as an MRI scan
  • examinations have been carried out by a trained assessor experienced in prolonged disorders of consciousness

For a permanent vegetative state to be confirmed, the above criteria must apply and six months must have passed since the start of symptoms after a non-traumatic brain injury, or 12 months after a traumatic brain injury.

Page last reviewed: 06/06/2013

Next review due: 06/06/2015