Montpellier-based Alcediag, which specialises in innovative medical tests, expects its invention to have a big impact, as current methods can take up to seven years to diagnose the condition.
It says the test will be on the market this year.
Director Dinah Weissmann said: “We will be carrying out market tests in 2020 and we’re also applying for permission to market it in the US.”
The firm says it works because it has discovered markers in blood which show modifications in the functioning of the brain.
“We have identified biomarkers related to a person’s RNA [a molecule in the cell whose main job is to transport information stored in DNA to other parts of the cell]. Nothing can change in your DNA but your RNA can be modified by factors including environment, diet and medical treatments, and this is what we can identify in the test.
“With a blood sample, we can identify modifications of RNA which are specific to depression or bipolar depression.”
The blood test can distinguish between the two conditions, with depression characterised by sadness and hopelessness and difficulty concentrating, while bipolar people experience severe mood shifts, from depression to states of elation and hyperactivity.
The test can also show if a medicine is working.
“Until now, doctors had to wait several months before assessing whether a treatment was having the desired effect,” Dr Weissmann said.
“With this test, you can see in a week, meaning treatments can be faster and more effective.”
The test also allows doctors to monitor a patient’s condition after a treatment is stopped.
It is the first time doctors will have a biological tool to help them diagnose the condition.
“In France, most people are treated by their GP, who has little time to spend making a diagnosis,” said Dr Weissmann.
“A psychiatrist will have more time, but most people don’t see a psychiatrist and it can be hard to evaluate whether someone is suffering ordinary depression or a bipolar disorder, and the treatments are different.”
The current version of the Alcediag test involves having a sample taken at a blood test centre, but the firm is looking to develop other methods, such as a finger prick test to help GPs to diagnose the condition more easily.