New biomarker blood test could diagnose depression
Since everyone occasionally experiences symptoms of depression such as feeling sad, unmotivated and disconnected, the distinction between normal negative emotion and depression can be blurry. True clinical depression occurs when these feelings interfere with everyday life for weeks or longer. Currently, diagnosis of depression is based on clinical evaluation of reported symptoms. The quasi-subjective nature of depression diagnosis means that correct assessment of depression relies on the accuracy of the practitioner preforming the evaluation. Unfortunately, non-psychologists/psychiatrists misdiagnose depression in the majority of cases. This may be particularly problematic in rural areas where access to mental health providers trained to correctly diagnose depression may be limited. Misdiagnosis delays proper treatment. Furthermore, this symptom-based approach to diagnosis leads people to claim that depression is not a real medical illness, which can lead to poor treatment compliance and stigma associated with this disease. These issues have made the search for purely objective measures of depression a priority and a new biomarker test may finally be making an objective test a reality.
Biomarkers measure pathological biological processes or pharmacological treatment response. The importance of biomarkers in medicine is reflected in the increase of their market worth. While the use of biomarkers in depression diagnosis is not a new venture, the clinical applicability of these tests has been limited by poor sensitivity and specificity.
Ridge Diagnostics, which holds numerous patents on blood-based tests for depression (some under its former name Precision Human Biolaboratory), may have moved one step closer to a clinically applicable test for depression. Researchers hypothesized that pooling data from a variety of biomarkers could improve the sensitivity and specificity of biomarker tests. The first step was to determine the minimal amount of relevant biomarkers to accurately determine depression. To address this, they screened 110 serum-based molecules believed to play a role in the biology of depression including inflammatory processes, neurotrophic factors (i.e. factors that promote development, survival and function of neurons), stress hormone response and metabolic processes. Nine markers emerged that provided maximal separation of depressed individuals from healthy controls. They then tested the accuracy of this test and found it able to correctly detect depressed individuals 90 percent of the time and controls 80 percent of the time.
While further replication in larger samples is needed, this test appears to be a promising diagnostic tool for depression. Researchers hope that further tests could distinguish the depressed state of bipolar disorder from unipolar depression, provide information on the course of illness, identify individuals vulnerable to depression or relapse, and track treatment response. Currently, Ridge Diagnostics offers blood-based depression tests in Southern California and North Carolina. They expect to expand availability throughout the country in 2013.
Treatment response is another area where progress is being made with biomarkers. In depression, predicting and preventing relapse is extremely important because each relapse increases the risk for future relapse by 16 percent. Using fMRI, researchers at the University of Toronto found that non-symptomatic previously depressed individuals that go on to relapse show increased activation in the medial prefrontal gyrus in response to sad videos. This indicates that individuals vulnerable to relapse can be predicted during asymptomatic states, which could be used to guide treatment research. While this research is promising, it is unclear as to the clinical applicability of this test. Imaging-based assessment, as compared to blood based, would be limited by the cost and time associated with the use of scanning machines. Understanding and predicting relapse, however, could improve research into treatment of depression.
Currently, mental disorders such as depression are diagnosed via subjective clinical evaluation. These subjective evaluations have been limited by accuracy in diagnosis and ability to predict treatment response. Recent advances in blood-based biomarkers appear clinically applicable as a diagnostic tool and neuroimaging of treatment response could hold potential to determine treatment response.