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Testing and Diagnosis

Reviewed by: HU Medical Review Board | Last reviewed: September 2023

Major depressive disorder (MDD), sometimes referred to as depression, is a clinical diagnosis. This means there are no specific tests that doctors can use to diagnose it. Instead, doctors rule out other causes of symptoms one by one. They also use information from your health history, physical exam, and screening tests to make a final diagnosis.1-3

There are several possible medical causes of depression-like symptoms. The medical issues doctors look for first depend on the person’s health history and symptoms. These medical causes may include:1,2,4

  • Thyroid disorders
  • Diabetes
  • Neurological issues, like stroke, multiple sclerosis, seizure disorders, or Alzheimer’s disease
  • Electrolyte imbalances, especially of calcium and sodium
  • Drug side effects, especially from steroids, blood pressure drugs, anti-seizure drugs, or sedatives
  • Withdrawal from alcohol or recreational drugs
  • Low levels of certain vitamins and minerals, like vitamin D, B12, B6, folate, or iron
  • Chronic inflammation from autoimmune disorders, infections, or cancers

If there is no obvious medical cause for symptoms, doctors will then consider making a mental health diagnosis.

Who starts the path to diagnosis?

Although MDD is a mental health condition, it is often diagnosed and treated by primary care doctors. They start by taking a full history of symptoms. This is called a health history. They will also do a physical exam. If they have concerns about certain symptoms, they may do further testing. These tests might include blood tests or body imaging scans.3,4

Many primary care and family medicine offices screen for depression during regularly scheduled visits. They use questionnaires that ask about depression symptoms. An example is the Patient Health Questionnaire-9 (PHQ-9).4,5

Emotions and moods can be hard to talk about sometimes. By giving you these screening tests, your doctor can determine whether mood-related symptoms are affecting you, even when they are not the reason for your visit. This can help prevent depression from going undiagnosed.4,6

In some cases, mood-related issues may be hard to diagnose and treat. Also, symptoms of multiple mental health conditions can overlap. If your primary care doctor suspects a mental health diagnosis, they may send you to a psychiatrist. A psychiatrist is a doctor who specializes in mental health conditions.7

Completing a health history

The first step at most doctor’s appointments is a health history. This is when your doctor asks about your recent experiences and any symptoms or concerns you are having. Your doctor will also ask about your past medical history, family history, and any drugs you take. Some possible questions are:1,2

  • What symptoms are you having?
  • Have these been the same or changed over time?
  • Does anything make them worse or better?
  • How long have you been noticing these issues?
  • What other medical conditions do you have?
  • What other health issues run in your family?
  • Does anyone in your family have a history of similar symptoms?
  • What concerns you the most about your symptoms?
  • What drugs (including over-the-counter drugs) are you taking?

These questions can change based on what symptoms you are having. They can also change based on the type of doctor you are seeing. Your primary care doctor may ask broader questions about your general health. A psychiatrist, on the other hand, may ask more in-depth questions about your mental health.7

Physical exam

After taking your health history, most primary care doctors will complete a physical exam. This includes using a stethoscope to listen to your heart, lungs, and belly. They will also check your vital signs, like blood pressure, temperature, and heart rate. They may do a basic neurological exam, too. This exam tests things like reflexes, coordination, vision, hearing, and sensation.1-3

Mental status exam

If you are seeing a psychiatrist, they may not do as thorough of a physical exam as your primary care doctor. This is because they are looking specifically at your mental health. Instead, they often do a mental status exam (MSE).8

An MSE is a way to assess your mood, thinking, behavior, and more. The MSE is a psychiatrist’s version of a basic physical exam by your primary doctor. Common areas your psychiatrist will look at during an MSE include your:8

  • Speech
  • Thought process and content
  • Mood
  • Insight into your current situation
  • Appearance
  • Motor function (how your body moves)
  • Perception of the world around you
  • Basic intelligence
  • Thoughts about hurting or killing yourself or someone else

They may be assessing many of these factors without you even realizing it. Your doctor may make mental notes about them while you are telling them about your life or symptoms. For example, if you are able to describe the way you are feeling and your concerns in a clear way, your doctor can see that your thought processes are functioning well.1,8

Blood tests and imaging

Although there is no single test for depression, your doctor may do blood or urine tests to rule out other medical causes of your symptoms. Common blood and urine tests include:1-4

  • Chemistry panel – Looks at electrolyte levels, like calcium or sodium
  • Complete blood count (CBC) – Looks for changes in infection-fighting blood cells
  • Liver function tests
  • Thyroid function tests
  • Tests for specific infections like HSV (the herpes virus), syphilis, or HIV
  • Vitamin level test
  • Urinalysis – Looks for urinary tract infections or other changes
  • Urine drug screening

Using these tests to rule out other conditions can help get a diagnosis of depression. In some cases, though, blood work is not enough. Your doctor may then order body imaging.1

These imaging tests may include computed tomography (CT) or magnetic resonance imaging (MRI) scans. These scans are usually of the brain. However, your doctor may order scans of other body parts depending on your symptoms.1

DSM-5 criteria

To make a final diagnosis of depression, your primary care doctor or psychiatrist will use the DSM-5 criteria. The DSM-5 is the fifth edition of a reference book called the Diagnostic and Statistical Manual of Mental Disorders. It lists many different mental health conditions and their symptoms.9,10

In the DSM-5, each condition has a specific set of symptoms that a person must have in order to be diagnosed with that condition. Screening tests like the PHQ-9 are designed to ask about these symptoms.9,10

In order to be diagnosed with MDD, a person must have at least 5 of the following 9 symptoms for 2 weeks or more at a time. These symptoms must also get in the way of daily functioning. They must not be due to another medical cause or mental health condition. The 9 main symptoms of MDD are:1,2,9

  • Low or depressed mood
  • Loss of pleasure in things you once enjoyed (anhedonia)
  • Weight changes
  • Not being able to sleep (insomnia) or sleeping too much (hypersomnia)
  • Changes in the speed of movements (faster or slower)
  • Low energy or fatigue
  • Feeling guilty or worthless
  • Trouble thinking or concentrating
  • Regularly thinking about death or planning for death

In order for an MDD diagnosis to be made, at least 1 of a person’s symptoms needs to be a depressed mood or loss of pleasure. You and your doctor will discuss your symptoms and their potential causes. If your doctor diagnoses you with MDD, they may recommend starting treatment with drugs, talk therapy, or both.2,9

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