• Doctors currently diagnose bipolar disorder with a clinical examination.
  • Recent studies have explored the levels of brain-derived neurotrophic factor in blood samples in cases of bipolar disorder and major depressive disorder.
  • A new blood test could support a clinical diagnosis of bipolar disorder. However, the diagnostic criteria remain unchanged.

Recent studies have given new hope of a potential test to diagnose bipolar disorder based on levels of a molecule in the blood. This research shows promise for future developments, although clinical evaluation will likely remain the cornerstone of diagnosis and treatment in the near future.

Researchers don’t know the root cause of bipolar disorder. It appears to be influenced by a combination of a few factors:

  • Genetics. Certain genes may predispose people to bipolar disorder. Someone is more likely to develop it if they have a close relative with bipolar disorder or depression.
  • Brain structure and function. Brain chemicals like norepinephrine, serotonin, and dopamine play a role in many neurological differences, including psychiatric and mood differences. Researchers have also found that the size and structure of some parts of the brain might be slightly different in those with bipolar disorder, according to the National Alliance on Mental Illness.
  • Stress. Significant stress can trigger mania in someone with genetic predisposition. A divorce, financial problems, major illness, and the death of a loved one are all examples of stressors that may lead to the onset of bipolar disorder.

As doctors learn more about what causes bipolar disorder, there may be new advances in diagnosis and treatment.

Doctors diagnose bipolar disorder on the basis of a clinical evaluation. It may consist of an interview and discussion about experiences, symptoms, and progression of those over time. There must be at least one episode of mania or hypomania for a diagnosis of bipolar disorder. Doctors then assess the severity of those episodes to determine the type.

A doctor may also perform a physical exam and run blood work. They do this to rule out other potential causes for symptoms aside from bipolar disorder.

One major challenge for doctors is distinguishing between unipolar and bipolar depression. Unipolar depression is also called major depressive disorder (MDD) and has the same criteria as bipolar depression. History of mania or hypomania along with depression is part of the diagnostic criteria for bipolar disorder, of which there are several types.

Your doctor can’t diagnose bipolar disorder from a brain scan or blood test. However, new research has uncovered a possible link between the expression of a key brain molecule and the diagnosis of mood disorders.

Blood testing as a basis for the diagnosis of bipolar disorder or depression is still in its early stages. But there has been promising research in the past few years.

Recent studies have explored the role of brain-derived neurotrophic factor (BDNF). This molecule has a big impact on learning and memory. Its expression, however, is complex. Scientists have found links between mood disorders and the levels of proBDNF and mBDNF in the blood.

A 2017 study of 105 participants found levels of mBDNF in the blood of people with bipolar disorder was lower than in those with MDD. Further, the ratio between mBDNF and proBDNF in the bipolar disorder group was also lower than in those with MDD.

The researchers noted this was a promising development, as people with bipolar disorder are often misdiagnosed with MDD. A blood test therefore could help identify those with bipolar disorder experiencing depressive episodes.

A 2021 study of a new assay test showed it’s possible to diagnose low blood mBDNF levels in people with MDD or bipolar disorder within an accuracy rate of 80 to 83 percent.

It may seem like an exciting development that a simple blood test can potentially diagnose bipolar disorder. But when asked if a blood test can provide conclusive evidence of bipolar disorder, Dr. Jeffrey Ditzell, a psychiatrist in private practice in New York City, answers in the negative.

“Not yet. The test assay is currently being used to differentiate proBDNF that is potentially neuroinflammatory, from (mature) mBDNF that is considered neuroprotective,” Ditzell told Healthline.

The test uses a cutoff for serum mBDNF levels of fewer than 12.4 nanograms per milliliter. This represents progress from previous tests, offering support for a clinical diagnosis of MDD or bipolar disorder.

However, Ditzell goes on to say that the blood test is unlikely to shift the diagnostic criteria for bipolar disorder in the near future.

“The BDNF levels can be helpful, but the diagnosis of the condition of bipolar disorder remains a clinical one, and the tests, though supportive, should not be considered as confirmatory, at this time.”

Treatment for bipolar disorder often involves a combination of medication, psychotherapy, lifestyle changes, social and family support. It can take some time to find the right medication.

From this perspective, the idea of a blood test for bipolar disorder can offer some hope. The 2021 study found mBDNF levels were higher in those taking antidepressants. This suggests that perhaps a blood test can assess the effectiveness of some medications.

When asked if people with bipolar disorder undergoing treatment should ask for this kind of blood testing, Ditzell explains that the tests need further development.

“I don’t think we are there yet, but may hopefully be there in the future,” said Ditzell. “I would not rush out to ask for such a test, as it currently is of limited diagnostic value and may well be cost-prohibitive.”

Blood analysis of mBDNF levels can potentially help people with bipolar disorder and doctors achieve proper diagnosis and effective treatment. As this research is in its early stages, it is likely clinical evaluation will remain the basis for bipolar disorder identification and treatment for the time being.