Wednesday August 21 2013
One million people across the world commit suicide every year
The potential for a blood test to predict suicide risk has sparked much debate, with The Independent reporting that a "US study raises controversial prospect to identify people at risk".
The news is based on the results of a study that aimed to identify biomarkers that could be used objectively to assess and track suicide risk. A biomarker is a biological marker, such as a genetic variant, that can be measured to indicate normal or abnormal biological processes.
Researchers identified biomarkers for suicide risk by analysing blood samples taken from a small group of men with bipolar disorder. Blood samples were taken when the men both reported having suicidal thoughts and when they did not.
The researchers looked at the expression process of specific genes, where information from the genes is used to make products such as proteins. They identified genes whose expression was different when people did not have suicidal thoughts and when people did have suicidal thoughts.
Of these, the expression of a gene called SAT1 was the strongest biomarker of suicidal behaviour and thinking. SAT1 levels were found to be high in a small group of men who had committed suicide. SAT1 levels were also able to differentiate the number of hospitalisations due to suicidal thoughts in groups of men with bipolar disorder or psychosis.
This small preliminary study in men raises the possibility that a biochemical test for suicide could be developed. But it is very difficult to see the possible applications of such a test in practice, even if it is found to be effective.
People who are thinking about suicide often tend to be secretive about their intentions, so it is hard to imagine that they would voluntarily attend "screening tests". Outside of those who are being treated compulsorily, this research seems to add little to the real-world problem of suicide prevention.
Where did the story come from?
The study was carried out by researchers from the Indiana University School of Medicine, Indianapolis Veterans Affairs Medical Centre, Marion County Coroner's Office, Indianapolis, and The Scripps Research Institute, California. It was supported by the US National Institutes of Health Director's New Innovator Award and a Veterans Affairs Merit Award.
The study was published in the peer-reviewed journal Molecular Psychiatry. It is open access, meaning that it is possible to download the research paper for free on the journal's website.
This story was well covered in both the Mail Online and The Independent. Both papers point out some of the study's limitations, such as the small sample size, the fact that it was only conducted in men, and the need for the findings to be replicated in other studies. They also both included commentary from independent experts on suicide prevention.
However, neither news organisation seemed to grasp the difficulties in finding a possible practical use for such a test. If a person expresses suicidal thoughts, the value of giving them a blood test to "confirm" whether or not they are at risk seems highly questionable. It also raises many safety concerns, including the possibility of false-negative results, where a person is discounted as a suicide risk because their blood test results don't tally.
Whether or not this test will be considered as a possible screening tool for people with a diagnosed mental health illness also raises a host of other questions. Some of these issues include how practical a "suicide test" is – would people who are feeling suicidal voluntarily attend a screening appointment?
What kind of research was this?
This study used information from four small cohorts:
- men with bipolar disorder whose thoughts of suicide varied
- men who committed suicide
- two groups of men with bipolar disorder and psychosis who were studied to see if levels of the biomarkers identified could predict hospitalisation because of suicidal thinking or behaviour
What did the research involve?
To identify potential biomarkers for suicide, the researchers studied a group of nine men with bipolar disorder. The men had a baseline visit and three testing visits three to six months apart.
At each testing visit, participants were assessed using psychiatric rating scales, which included a rating for suicidal thoughts (suicidal ideation). Only men who had a change in suicide ideation score between testing visits from no suicide ideation to high suicide ideation were included.
The men also gave a blood sample at each visit. RNA – a molecule that transfers from the information contained in DNA to other cellular machinery – was extracted from the blood to see which genes were expressed. This was so the researchers could see which genes were being made into RNA, which is then used to make the gene product (for example, a protein).
The researchers looked at the genes that were expressed when the men had no suicide ideation and when the men had high suicide ideation. They did this by comparing the genes expressed in the same man when he had no suicide ideation and when he had high suicide ideation, and by comparing low and high ideation in different men.
The researchers combined the results of this study with our existing knowledge from human genetic and post-mortem brain examinations. This allowed them to identify the genes that are expressed more or less during high suicidal ideation.
The researchers then tested the genes identified by looking at the levels of expression in a cohort of nine men who had committed suicide by means other than overdose and who had not been dead for more than 24 hours.
The researchers then looked at whether levels of the genes they identified could predict subsequent hospitalisation with or without suicidal thoughts in a cohort of 42 men with bipolar disorder and a cohort of 46 men with psychosis.
A hospitalisation was categorised as being without suicidal thoughts if suicide was not listed as a reason for admission and no suicidal ideation was described in the admission and discharge medical notes.
A hospitalisation was considered to be the result of suicidal thoughts if an act of suicide or intent was listed as a reason for admission and suicidal ideation was described in the admission and discharge medical notes.
The distinction is important, as people who have psychosis or are bipolar are often admitted to hospital, but not always because of suicide risk. For example, a person may be hospitalised if a manic or psychotic episode means they risk harming themselves.
What were the basic results?
The study of the nine men with bipolar disorder identified SAT1 as the top high-risk suicide biomarker. SAT1 expression levels (levels of SAT1 RNA) were found to be increased in suicidal states.
When compared with low SAT1 levels, high levels could differentiate future and past hospitalisations owing to suicide in people with bipolar disorder.
This was also the case for the men with psychosis, although the association was weaker. This means, for example, that the researchers found that people with high SAT1 levels were more likely to have hospitalisations in the future because of suicide.
Levels of expression of three other genes (PTEN, MARCKS and MAP3K3) could also differentiate hospitalisation because of suicide.
When the researchers added information on anxiety, mood and psychosis to information on SAT1 levels, the ability to predict future hospitalisations related to suicide was improved.
Another biomarker called CD24 (CD24 molecule/small cell lung carcinoma cluster 4 antigen) was the top protective marker against suicide risk, as levels were found to be decreased in suicidal states.
In addition, 13 of the other 41 top scoring markers showed significant changes from no suicidal ideation to high suicidal ideation, to suicide completers. Differences in the levels of expression of six genes remained significant after correction for multiple comparisons.
How did the researchers interpret the results?
The researchers conclude that they have found "possible biomarkers for suicidality". They go on to say that the "results have implications for the understanding of suicide, as well as the development of objective laboratory tests and tools to track suicidal risk and the response to treatment".
This study raises the possibility that a test for suicide could be developed. However, the research is still in its preliminary stages.
The current study was small and only included men. It also only involved men with bipolar disorder or psychosis. The findings of this study need to be replicated in other studies, but even then it is difficult to see what the practical applications of such a test would be.
The reasons why a person thinks about or attempts suicide or self-harm are highly complex. Being at risk of suicide may involve a combination of various life events and genetics. Financial concerns, loss of work, relationship breakdown or bereavement, as well as health factors, can all influence a person's mental health.
A person's risk may also be increased when more than one negative life event occurs at the same time or there is a trigger event, such as losing a job or a relationship coming to an end.
People with a mental health illness such as depression, bipolar disorder or schizophrenia may be at an increased risk of suicide, particularly if they have a history of attempting suicide or self-harm.
But suicide does not only occur in people with a diagnosed mental health illness. People may have suicidal thoughts but have not been formally diagnosed with a mental health illness, or those who have received a diagnosis may not be receiving care and treatment.
Overall, even if further studies gave positive results, the possible application of such a blood test as a screening tool for suicide risk raises extensive questions.
The main issue is whether the results of a blood test, which does not take account of the many psychosocial factors that may be involved in a person's thoughts about harm or suicide, could ever provide a reliable indication of a their actual feelings or intent.
The most important thing is that people who have thoughts about self-harm or suicide immediately receive the support and care that they need. People who are having these thoughts should talk to someone they trust, such as a loved one or their GP.
There are also many helpline support groups available, such as the Samaritans, who can be reached on 08457 90 90 90.
Analysis by Bazian. Edited by NHS Choices. Follow Behind the Headlines on Twitter.