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Can blood test show mental illness?

Mental illness has long been a challenge to diagnose accurately and objectively. Doctors must rely on patient descriptions of thoughts and behaviors, information from family and friends, and observable symptoms. This leaves a lot of room for uncertainty and misdiagnosis. But what if a simple blood test could reveal biological markers of mental illness? Emerging research suggests that specific biomarkers in the blood may someday allow objective diagnosis of conditions like depression, bipolar disorder, and schizophrenia.

What are biomarkers?

Biomarkers are biological characteristics that can be measured objectively. They indicate specific disease processes in the body. For mental illness, researchers hope to identify biomarkers that signify the underlying biological abnormalities or vulnerabilities that contribute to psychiatric disorders. Potential biomarkers being explored include:

  • Inflammatory proteins
  • Stress hormones
  • Neurotrophic factors that regulate neuron health
  • Metabolic products
  • Genes and gene expression products

Finding consistent, reliable patterns of biomarkers could allow straightforward lab testing to reveal or confirm psychiatric diagnoses. This would provide an objective measure to complement the subjective symptoms reported by patients. Here is a summary of the potential benefits:

Potential Benefits of Biomarker Blood Tests for Mental Illness
  • Objective, definitive diagnoses
  • Earlier detection, before symptoms escalate
  • Monitoring of disease progression and treatment efficacy
  • Personalized treatment based on biological profile
  • Easier differentiation between disorders with overlapping symptoms

Research on inflammation biomarkers

One prominent area of research focuses on inflammatory biomarkers. Increased inflammation seems to be involved in depression and may trigger or worsen characteristic symptoms like low mood, fatigue, poor concentration, and sleep disturbance. Levels of inflammatory proteins called cytokines are repeatedly found to be elevated in patients with major depressive disorder (MDD).

For example, a 2012 meta-analysis compiled data from 24 studies comparing blood levels of the cytokine interleukin-6 (IL-6) in people with and without depression. Across all studies, patients with MDD had significantly higher IL-6 levels than non-depressed controls. This suggests inflammatory processes are abnormally active in depression.

Other studies find connections between depression and inflammatory factors like the cytokine TNF-alpha and the acute-phase protein c-reactive protein (CRP). Testing for an inflammatory biomarker signature could potentially confirm suspected depression. It could also reveal an inflammatory component driving symptoms in other ambiguous psychiatric conditions.

Limitations of inflammation testing

While the inflammation link is promising, there are limitations:

  • No single biomarker is definitive for diagnosis yet.
  • Inflammation alone does not always equate to depression.
  • Levels can be influenced by other medical conditions.
  • Severe mental illness can occur without inflammation.

Researchers caution that inflammation biomarkers should augment clinical interview information, not replace it entirely. But used judiciously, they can add objective data to support a diagnosis.

Blood tests for schizophrenia

Schizophrenia is another psychiatric disorder where diagnostic blood tests are being researched. Multiple studies associate schizophrenia with altered levels of various biomarkers, including:

Potential Blood Biomarkers for Schizophrenia
  • Inflammatory cytokines
  • Oxidative stress markers
  • Brain-derived neurotrophic factor (BDNF)
  • Dopamine metabolites

However, no definitive diagnostic test exists yet. Schizophrenia is biologically complex, with overlaps in biomarkers across psychiatric conditions. But patterns of certain markers may eventually help distinguish schizophrenia from bipolar disorder or major depression.

Genetic testing

Genetics are strongly linked to schizophrenia risk. Certain gene variations, while not determinative alone, increase vulnerability. Testing gene expression in white blood cells can identify a “signature” linked to schizophrenia. A 2015 study found a set of 33 genes that were over- or under-expressed in schizophrenia patients compared to healthy controls.

While not yetready for diagnostic use, gene panels may eventually help assess schizophrenia likelihood. Genetics will likely need to be combined with other biomarker data to be clinically meaningful.

Research on bipolar disorder

Bipolar disorder is characterized by swings between high and low mood states. Research seeks biomarkers related to the underlying disease processes provoking these mood fluctuations. Possible markers include:

Potential Blood Biomarkers for Bipolar Disorder
  • Inflammatory cytokines
  • Oxidative stress markers
  • Cortisol
  • Melatonin
  • Norepinephrine
  • Folate
  • Gene expression profiles

The presence of manic and depressive episodes in bipolar disorder often confuses diagnosis. Biomarker profiling could help distinguish bipolar disorder from unipolar depression. Combinations of gene variants, hormones, cytokines, and neural signaling molecules may one day provide a signature to positively identify bipolar disorder.

Monitoring treatment with biomarkers

Once diagnosed with bipolar disorder, biomarkers could help guide treatment choices and monitor outcomes. Lower blood levels of inflammatory cytokines or oxidative stress markers could show anti-inflammatory medications are effectively targeting relevant disease processes. Certain biomarkers increasing or decreasing over time may signal emerging manic or depressive symptoms before full-blown episodes occur.

This could allow preventative treatment adjustments. Biomarkers could verify medications are exerting their intended effects and enable truly personalized medicine tailored to each patient’s biology.

Challenges in developing diagnostic biomarkers

Progress toward clinically useful blood tests for mental illness is encouraging but faces hurdles. Challenges researchers still need to address include:

Challenges in Developing Reliable Diagnostic Biomarkers
  • No single biomarker is specific for one disorder.
  • Overlap between psychiatric conditions.
  • Variability between individuals.
  • Influence of factors like medication, diet, and medical illness.
  • Need for large, diverse sample sizes.
  • Lack of biomarker standardization between labs.

Developing sensitive, standardized tests that provide meaningful diagnostic and treatment guidance remains difficult. Researchers need to identify biomarker profiles across larger, more diverse populations. Sophisticated analysis is unraveling how different biomarkers interact to create “biosignatures” characteristic of specific disorders.

The future of diagnostic blood testing

While still in the research realm, initial results on blood biomarkers for mental illness are encouraging. Ongoing advances in genetics, neuroscience, and lab techniques are accelerating progress. Biomarker testing will likely become integrated into psychiatry in the future, though not as a wholesale replacement for clinical evaluation.

Instead, blood tests can add objective data to confirm diagnoses, uncover biological drivers, predict treatment responses, and enable personalized care. Combining biomarker profiles with machine learning algorithms may eventually allow accurate screening and monitoring. This could expand access to mental health evaluation and optimize treatment. Realistically, blood-based diagnostic testing remains years away from mainstream clinical use. But the need is great, and research momentum continues building.


Mental illness has proven difficult to diagnose accurately based on symptom descriptions alone. But emerging research on biological biomarkers in the blood brings hope for objective tests. Measurements of inflammatory proteins, hormones, neural regulators, metabolites, and gene expression may reveal signatures characteristic of disorders like depression, bipolar disease, and schizophrenia. While still investigational, biomarker testing could someday confirm diagnoses, predict treatment response, and improve personalized care. With continued research progress, blood-based diagnosis of mental illness may become a clinical reality. But current limitations must still be overcome to develop sensitive, reliable biomarker testing. While not an immediate panacea, this growing field represents an exciting frontier in the evolution of psychiatric diagnosis and treatment.