The mental disorder schizophrenia could be easily diagnosed by a blood test, say researchers.

Diagnosis at present relies on psychiatric assessment and correct reporting of symptoms by patients.

The changes in the brain which lead to the condition are still very much a mystery to doctors.

Many research findings suggest a link between levels of a body chemical called dopamine, and the number of receptors to the chemical on the surface of nerve cells.

Post-mortem results on these nerve cells suggests that the number of these receptors may be increased in schizophrenic patients.

Even a certain type of scan can measure the number of these receptors in live patients, but without sufficient precision.

Blood molecule

Professor Sara Fuchs, writing in the Proceedings of the National Academy of Sciences, believes she has found another way of finding out.

There are also dopamine receptors on the surface of white blood cells called lymphocytes.

The research team compared the number on the blood cells of diagnosed schizophrenics with the number on the blood cells of healthy individuals.

Even checking the number of these receptors on blood cells is extremely difficult, however, and the team, from the Weizmann Institute in Israel, found a way of testing the levels of molecules which control the formation of the receptors.

A statistical analysis showed that the blood of patients with schizophrenia on average contained 3.6 times more of these molecules, called D3 messenger RNA molecules, than the blood of healthy people.

The scientists suggest that this blood test may be able to give a reliable indication of when a patient could have schizophrenia.

Approximately 1% of the population is thought to have the condition, which can manifest itself in a number of ways, including hallucinations or delusions.