The lack of objective medical tests in psychiatry is a common criticism of the field. According to some, being a doctor means using physical exams, lab work or imaging to evaluate patients. Indeed, oncologists can find a tumor on a CT scan. Cardiologists can diagnose a heart attack with blood tests or an electrocardiogram.

Despite public misconceptions, psychiatrists do much of the same. We use objective tests all the time to evaluate patients with mental illness. (And I don't mean inkblots.)

Say a middle-aged man visits a doctor's office because he's been experiencing confusion and memory problems. His family says his speech sounds different. The man has become delusional about his neighbors, convinced they are poisoning his food. He has no other medical history, other than a rash on his genitals years before.

A century ago, doctors might have diagnosed him with "general paresis of the insane." He might have been confined to an asylum and left in squalid conditions. Yet  today, we know this disorder by another name—neurosyphilis. It's a neuropsychiatric disorder caused by the presence of bacteria that cause syphilis in the brain. We can send off a lab test to identify this disease, and penicillin often cures patients.

This is far from the only example. In the 19th century, a German neurologist named Carl Wernicke found a series of three patients—two of whom were alcoholics—who suffered from strange symptoms including impaired eye movements, confusion, and poor balance. Around the same time, a Russian psychiatrist named Sergei Korsakoff discovered that patients with chronic alcoholism sometimes developed peripheral neuropathy, memory impairment, and psychiatric disturbances. Both physicians published papers describing these disorders, and the overlapping conditions later came to be known as Wernicke-Korsakoff syndrome.

In the years following, medical professionals identified more and more patients with these findings. But no one knew what caused the symptoms. The syndrome was often referred to as "alcoholic insanity." Decades of research and the Nobel Prize-winning work of Dr. Christiaan Eijkman helped identify a vitamin called thiamine,, the deficiency of which was eventually found to be the cause of these conditions. We now routinely treat alcoholic patients with thiamine to prevent Wernicke-Korsakoff syndrome, and scans like brain MRI help confirm the diagnosis.

In psychiatry, we use blood work and imaging every day to evaluate patients with symptoms of mental illness. A vegan suffering from crippling depression might have B12 deficiency, while a patient who abuses IV drugs with progressive delusions and aggression could have HIV encephalopathy. A college student with anxiety, palpitations, and sensitivity to heat would raise alarms for hyperthyroidism.

This is a common theme in the history of psychiatry. Disorders treated under the domain of mental illness cross over into the realm of other medical specialties once an underlying cause is discovered. A patient might seek treatment for mental health issues, but once a medical reason for these symptoms is found, other doctors often then assume their care. "We'll take it from here," our colleagues say.

So the purview of psychiatry has largely remained limited to diseases that defy explanation. Our specialty has been relegated to the medicine of the unknown. We can't yet test your blood for schizophrenia. We're unable to diagnose bipolar disorder on imaging. We're left with the Diagnostic and Statistical Manual of Mental Disorders and its inherently subjective criteria for defining illness.

Over the coming decades, research into the brain will drive mental health diagnoses and treatment in new directions. Yet what happens to the field of psychiatry as we continue to discover the underlying causes of mental illness? Does its scope of practice shrink ever further? Does the specialty fade further into irrelevance?

For example, recent studies have found associations between mania and elevated uric acid levels in the blood. Giving medications (e.g., allopurinol) that lower serum uric acid for bipolar patients with mania has been found to improve treatment responses in randomized placebo-controlled trials. If this relationship were to be true, could bipolar disorder become another everyday medical condition, just like gout?

Scientists have taken similarly unique approaches towards tackling depression. Some have proposed that depression might be caused by autoimmune responses to infection, as depressed patients are often fatigued with low appetite and other symptoms commonly seen among infected patients. What's more, depressed patients commonly have elevated inflammatory markers in their blood. Might depression one day be treated by autoimmune specialists? Could immunotherapies eventually cure the blues?

One day, we'll find out and, depending on the answers, you may be visiting a different kind of doctor for your mental health. If you happen to see a psychiatrist though, don't be surprised if we ask you to stop by the lab on your way out.