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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.

Doctors can score a person's level of consciousness using a tool called the Glasgow Coma Scale.

This assesses 3 things:

• eye opening – a score of 1 means the person doesn't open their eyes at all, and 4 means they open their 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.

Other scoring systems

There are also more specific scoring systems based on more detailed observations of a person's behaviour.

One example is known as the JFK Coma Recovery Scale-Revised (CRS-R).

This system uses 23 different items, each with individual scales to assess how a person is responding.

Brain scans are used to help assess the level of brain damage in someone with impaired consciousness. 

They can also check for signs of any complications, such as hydrocephalus (a build-up of fluid in the brain).

There are several types of scans that can assess brain structure if thought appropriate, such as a CT scan or an MRI scan.

fMRI scans

There are separate scans that can show areas of brain activity as well as brain damage.

One example is a functional magnetic resonance (fMRI) scan.

An fMRI scan is able to show changes if the brain is responding to light and sounds.

But they don't necessarily show awareness, as the brain is able to respond to stimulation even without the person actually being aware of it.

fMRI scans are not routinely used by the NHS in diagnosing disorders of consciousness.

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's 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's been confirmed drugs or medication aren't responsible for the symptoms
• it's been confirmed treatable problems with the body's chemistry (a metabolic disorder) aren't 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
• examinations have been carried out by a trained assessor experienced in prolonged disorders of consciousness

A permanent vegetative state can usually be diagnosed with confidence if:

• the above criteria have been met, and
• at least 6 months have passed since the start of symptoms and there have been no signs of improvement