How is mental illness diagnosed

A full medical history should be taken and information about recent changes in the person's life should be obtained from family and/or friends. Usually one or more of these people will be involved in providing care for the relative with mental illness, and as a result will have an understanding of how the person's condition has developed and the extent of the symptoms, and the impact it is having on quality of life.

It will be important for the psychiatrist to check that the symptoms are not part of some other medical syndrome, or other explainable cause (see physical causes of mental illness). This is because some symptoms found in mental illnesses, such as hallucinations, can also appear in other medical conditions. The psychiatrist should gather all observations together, and then eliminate any other possible cause.

This process is not always easy, and it is not uncommon to have difficulties in either getting it recognised that you do have a mental illness, getting access to care and treatment, or that you may feel you have been given a misdiagnosis.

Many different mental illnesses have overlapping symptoms and so it can be difficult to tell the conditions apart. Reaching a diagnosis can be difficult and it takes time to be sure that the individual's symptoms truly indicate a particular mental illness. Family and friends can and should be involved, as they will be aware of details of family intimacies, cultural differences and religious beliefs. They may well be able to confirm to the professional that a desire for contact with a church, for example, is not a sudden change brought on by illness, but a part of the person's previous upbringing and normal routine.

There is hope that in the future, scans of the brain or some other test will be used to confirm the presence of specific mental illnesses.

• Brain scans

Neurological changes occur in the brains of people with most mental illnesses. Some of these can be seen using brain imaging techniques. It may be possible in the future to use brain imaging to make a diagnosis. However, this is not yet possible.

• Niacin flushing test

This is a test that is being developed for schizophrenia. It is currently still at the research stage, and is not accepted as a standard test for schizophrenia. The test works by measuring the level of particular fatty acids in the body as people with schizophrenia are often found to have reduced levels of these. (This reduction is believed to affect some of the nerves in the brain and so suggested as a possible cause for schizophrenia)

The test is believed to work in that one effect of the reduced levels of fatty acids is in the way blood vessels can be made to dilate and the skin become flushed by the vitamin niacin. When a solution of niacin is painted on the skin the blood vessels will dilate and the skin will become flushed, but this will not happen in a person with reduced fatty acid. However, just as not all people with a diagnosis of schizophrenia have reduced levels of fatty acid, not all people will respond to the test.