Blood Test Could Improve Diagnosis of Depression

By: Michael Ferguson
Thursday, April 30, 2015
Specialty: 

Researchers may have developed a blood test to diagnose depression in adults.

For the roughly 25 million American adults who the National Alliance on Mental Illness estimates are affected by major depressive disorder (MDD) annually, the prospect of more accurate diagnosis is a boon. If further clinical trials confirm its viability, the first objective diagnostic tool for MDD may soon become ubiquitous in primary care offices.

Eva E. Redei, PhD, David L. Stein Professor of Psychiatry in the Department of Psychiatry and Behavioral Sciences at Northwestern University’s Feinberg School of Medicine, along with a team of researchers at the school, developed the blood test.

“When there is suspicion of a cardiovascular disease, several tests are done to know the degree and nature of it,” Redei says. “Hopefully, it will be the same for depression.”

Adding the test to a primary care physician’s armamentarium could potentially improve MDD care in the same way blood tests and statins revolutionized cardiovascular care.

“Any indication for depression in a clinical environment could prompt the health professional to order a blood test for MDD,” Redei says. “Then the results, together with all the other information obtained, would be interpreted by the health professional — just like for any other medical [condition].”

Diagnostic Challenge

Without such a tool, psychiatrists rely on patients’ self-reports for diagnoses. But because many symptoms associated with MDD can also be evidence of other psychiatric conditions and self-reports are far from definitive proof, diagnosis is essentially left to a mental health professional’s judgment.

“Depression is an illness, just like other illnesses. It can be objectively diagnosed. A non-psychiatrist can be helped by this objective test as well, as we know that depressed patients are seeing more physicians more times than non-depressed patients.”
— Eva E. Redei, PhD, David L. Stein Professor of Psychiatry in the Department of Psychiatry and Behavioral Sciences at Northwestern University’s Feinberg School of Medicine

“Current methods are based on a scripted psychiatric interview with the patient and [depend on] the psychiatrist’s or psychologist’s expertise to interpret the patient’s behavior,” Redei says. “So, if the patient is not able or willing to describe the symptoms, and/or the health professional does not have extensive knowledge of the illness, depression would be over- or under-diagnosed.”

Clinicians have long recognized the limitations of existing diagnostic approaches. For instance, addressing diagnosis of depression among patients with advanced metastatic cancer, a September 2000 article in Postgraduate Medical Journal noted: “[U]p to 80% of the psychological and psychiatric morbidity which develops in cancer patients goes unrecognised and untreated. One of the main difficulties in establishing a diagnosis of an illness where there are no biological markers, physical signs, or diagnostics tests is deciding what can be called ‘appropriate sadness’ as patients approach the end of life and what is a depressive illness.”

Predictive Potential

The newly developed blood test measures the level of nine RNA markers that were found to be significantly different at baseline between participants in the control group and those who had previously been independently diagnosed with MDD. Identifying the range within which RNA markers typically register in healthy patients enables psychiatrists to diagnose MDD with the blood test — similar to diagnosing high cholesterol or diabetes.

Over an 18-week period, depressed participants in the study underwent cognitive behavioral therapy (CBT) sessions in person and by phone. CBT is often used along with medications and, in severe cases, electroconvulsive therapy. Researchers tracked the RNA marker levels throughout and found that changes in three markers correlated with positive response to therapy.

Some patients did not respond to CBT, and researchers returned to baseline RNA marker levels to evaluate whether there was evidence that the test could also serve as a predictor of therapeutic success. They found that it did, as patients who responded positively to CBT had a distinct pattern of marker levels.

The new blood test may offer psychiatrists the opportunity to more individually craft treatment plans for patients with MDD and potentially increase the efficacy of therapy.

Further Applications

In addition, the test’s evaluative capabilities might reach beyond CBT success rates. Three RNA markers are concentrated in a specific way in depressed patients — regardless of the resolution of MDD after therapy.

“Three blood markers showed depressed levels in some of the patients, even after they remitted,” Redei says. “That suggested that these markers show susceptibility to depression, and that patients showing these patterns may likely have another episode of MDD. [These patients] should be closely monitored, and perhaps treated with psychotherapy or antidepressants, as is frequently done in patients with recurrent depression. However, if these markers are confirmed, they could identify patients with susceptibility even before the next episode occurs.”

Redei, who previously developed a similar blood test to identify MDD in teenagers, expanded the demographics in this study, enrolling patients between 23 and 83 years old. The three markers that differed between control participants and patients with MDD in the team’s current study also differed in the study geared to teens, confirming the role of the markers in pathological processes associated with depressed moods.

Redei and her team plan to expand study populations and determine whether the test can differentiate between unipolar MDD and bipolar depression.