Colleen Pearce heads the independent body the Victorian government set up to protect the rights of people with a disability. She said it was critical to identify impairments early on to ensure prisoners received effective support and to prevent them from reoffending when released, because there were higher and more severe rates of cognitive impairments in prisons than in the community.

''Without [routine screening], people with cognitive impairments can get trapped in a revolving door of endless contact with police and prisons with attendant costs to the community and, worse, the loss of their potential as contributing community members,'' she said.

Fairfax Media reported last month that up to half of state prisoners have an acquired brain injury, many undiagnosed.
Neuropsychologist Rachel Hutchens said acquired brain injuries, in particular, should be tested routinely. Dr Hutchens was involved in a five-year study that developed a screening tool for such injuries, which was commissioned by the Department of Justice in 2009. The study - conducted by La Trobe University and brain damage specialist Arbias - estimated that 42 per cent of men and 33 per cent of women in the prison population had an acquired brain injury.

Dr Hutchens said the tool was more effective because it included questions about not only previous assaults and car accidents, but also alcohol and drug use, suicide attempts and overdoses.

''Those risk factors actually came out as being more prevalent than traumatic brain injury and are currently being ignored as real risks of causing acquired brain injury in the prison system,'' she said.

Arbias chief executive John Eyre said that while some prison officers had undergone the two-hour training course required to use the tool at the time of the study, the Department of Justice had not approached Arbias for further training since then.

''That leads me to suspect that if they are using the tool they may not be using it correctly, or alternatively they're not using it,'' Mr Eyre said.

A Department of Justice spokeswoman said that different screening tests were available, but most prisoners were tested with the Victorian Intervention and Screening Assessment Tool.

This identified potential impairments, which were then confirmed by a neuropsychologist or clinician. She would not say whether people on remand were similarly tested.

Margot Powell, a senior solicitor at the Mental Health Legal Centre, which provides free representation for mentally ill people, said the greatest difficulty the centre's clients faced was obtaining appropriate psychiatric treatment and medication.

The Department of Justice spokeswoman said that everyone who entered prison was screened by a mental health care professional within 24 hours. Those shown to have a mental health problem were given a treatment plan that was reviewed regularly.