New blood test can improve diagnosis of bipolar disorder

A new blood test to improve diagnosis of bipolar disorder has been developed by researchers at the University of Cambridge

The researchers say the blood test on its own could diagnose up to 30% of patients with bipolar disorder, but that it is even more effective when combined with a digital mental health assessment.

Bipolar disorder affects 1% of the population, but about 40% of people with the condition have been wrongly diagnosed with major depressive disorder. By incorporating biomarker testing into the diagnostic process, doctors could differentiate more clearly between the two conditions, which have overlapping symptoms but require different pharmacological treatments.

The study, reported in the journal JAMA Psychiatry, shows that the blood test could complement existing psychiatric diagnosis and help researchers understand the biological origins of mental health conditions.

Patients had received diagnosis of major depressive disorder

The researchers used samples and data from the Delta study, conducted in the UK between 2018 and 2020, to identify bipolar disorder in patients who had received a diagnosis of major depressive disorder within the previous five years and had current depressive symptoms. Participants were recruited online through voluntary response sampling.

More than 3,000 participants were recruited, and they each completed an online mental health assessment of more than 600 questions. The assessment covered topics such as past or current depressive episodes, generalised anxiety, symptoms of mania, family history or substance abuse.

Of the participants who completed the online assessment, approximately 1,000 were selected to send in a dried blood sample from a simple finger prick. The researchers then analysed the samples for more than 600 metabolites (substances produced in the body during metabolic processes such as digestion). After participants then completed a standard diagnostic interview, 241 participants were included in the study.

Analysis of the data showed a significant biomarker signal for bipolar disorder, even after accounting for confounding factors such as medication. The identified biomarkers were correlated primarily with lifetime manic symptoms and were validated in a separate group of patients who received a new clinical diagnosis of major depressive disorder or bipolar disorder during the study’s one-year follow-up period.

Use of biomarker test improved diagnostic outcomes

The researchers found that the combination of patient-reported information and the biomarker test significantly improved diagnostic outcomes for people with bipolar disorder, especially in those where the diagnosis was not obvious.

Dr Jakub Tomasik, a senior research associate at the University of Cambridge, and first author on the study, said: “People with bipolar disorder will experience periods of low mood and periods of very high mood or mania. But patients will often only see a doctor when they’re experiencing low mood, which is why bipolar disorder frequently gets misdiagnosed as major depressive disorder.”

The most effective way to get an accurate diagnosis of bipolar disorder is a full psychiatric assessment. However, patients often face long waits to get these assessments, and they take time to carry out.

“Psychiatric assessments are highly effective, but the ability to diagnose bipolar disorder with a simple blood test could ensure that patients get the right treatment the first time and alleviate some of the pressures on medical professionals,” said Tomasik.

He added that some patients preferred the biomarker test, because it was an objective result: “Mental illness has a biological basis, and it’s important for patients to know it’s not in their mind. It’s an illness that affects the body like any other.”

Sabine Bahn, professor of neurotechnology at the University of Cambridge and a co-author on the study, said that the online assessment was “more effective overall, but the biomarker test performs well and is much faster. A combination of both approaches would be ideal, as they’re complementary.”

She said the biomarkers could also be used to identify potential drug targets for mood disorders, leading to better treatments.