An Irish-led study has found that testing the levels of certain proteins in the blood can predict whether a person at risk of psychosis is likely to go on to develop a psychotic disorder later in life.

Psychosis is a mental health problem that affects around 3% of the population. Common symptoms include hallucinations, delusions, and disordered thinking.

According to the scientists who carried out this study, based on certain criteria, such as mild or brief psychotic symptoms, some people are considered to be clinically at high risk of developing a psychotic disorder, such as schizophrenia.

However, only 20-30% of these people will actually go on to develop a psychotic disorder.

The scientists analysed blood samples taken from people who were considered to be at clinical high risk of psychosis. These individuals were followed up for several years to see who did and did not go on to develop a psychotic disorder.

After assessing the proteins in blood samples and analysing this data, the scientists were able to find patterns of proteins in the early blood samples that could predict who did and did not go on to develop a psychotic disorder at the time of follow-up.

Many of these proteins are involved in inflammation. This suggests that there are early changes in the immune system in people who go on to develop a psychotic disorder. The findings also suggest that it is possible to predict their outcomes using blood samples taken several years in advance.

The scientists, who were led by a team from the Royal College of Surgeons in Ireland (RCSI), found that the most accurate test was based on the 10 most predictive proteins. This test correctly identified those who would go on to develop a psychotic disorder in 93% of high-risk cases.

It also correctly identified those who would not go on to develop a psychotic disorder in 80% of cases.

"Ideally, we would like to prevent psychotic disorders, but that requires being able to accurately identify who is most at risk. Our research has shown that analysis of protein levels in blood samples can predict who is truly at risk and could possibly benefit from preventive treatments.

"We now need to study these markers in other people at high risk of psychosis to confirm these findings," explained the study's senior author, Prof David Cotter, of the RCSI.

Details of these findings are published in the medical journal, JAMA Psychiatry.