Diagnosing Depression: 5 Lab Tests You Need
Mental Health ConditionsDepression

‘I Feel Depressed. What Labs Do I Need and Why?’

‘I Feel Depressed. What Labs Do I Need and Why?’
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Published on September 29, 2026
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We often talk about depression like it’s one condition. But in reality, it’s a combination of symptoms with many causes. Some of these causes of depressive symptoms are psychiatric, such as major depressive disorder, bipolar disorder, or schizoaffective disorder. And some of these causes aren’t psychiatric at all — they’re related to physical illnesses.

Common medical conditions that can mimic depression include thyroid disease, anemia, vitamin deficiencies, glucose dysregulation, low testosterone, neurologic disease, and substance and medication use.

Because of these different factors, a medical workup, including laboratory testing, may be necessary to accurately diagnose depression. Although there aren’t labs that can diagnose the psychiatric causes of depression, there are labs for the medical causes. By testing for those potential causes and ruling them out, doctors can be more certain that the symptoms someone is experiencing are psychiatric and will respond to psychiatric treatments.

Here are five labs you need if you’re experiencing depressive symptoms. The good news is that your primary care doctor often orders these tests during your annual physical, so depending on when your last physical was, you may not need more lab testing. The labs may need to be repeated if they are older or if you have physical symptoms that are concerning for a certain condition.

1. Thyroid Panel

The thyroid is a small gland that makes hormones that help regulate energy, metabolism, heart rate, and body temperature. A thyroid panel is a group of blood tests that checks whether your thyroid is making the right amount of thyroid hormone. Too little or too much thyroid hormone can cause symptoms that overlap with depression, including changes in energy, sleep, concentration, appetite, and mood.

Research shows that the relationship between thyroid dysfunction and depression is complex.

 Not only can having too much or too little thyroid hormone mimic symptoms of depression, but thyroid disease itself is a risk factor for developing depression. That’s because having a chronic illness in general increases a person’s risk of depression, likely related to ongoing inflammation and other disease processes in the body, the stress of living with a chronic condition, and potential side effects of medications.

Checking thyroid hormone levels is important for depression management for two reasons: The symptoms someone is experiencing may be related to thyroid issues and not depression; and if thyroid disease is present in addition to depression, treating the thyroid condition may help make the treatment for depression more effective.

2. Complete Blood Count

A complete blood count (CBC) tests for the number of various blood cell types, including red blood cells (which carry oxygen around the body) and white blood cells (which help fight infection). Anemia is a condition that causes low red blood cells, which can lead to decreased energy, weakness, and fatigue, which some people interpret as depression.

Similar to thyroid disease, anemia can look like depression, and there is also an overlap between anemia and depression, with anemia increasing a person’s risk of developing depression.

Although no blood tests are technically required prior to diagnosing depression, practice guidelines generally acknowledge that testing for thyroid function and CBC are both low-cost, simple ways to rule out two common medical issues that can mimic depression.

3. Comprehensive Metabolic Panel

A comprehensive metabolic panel (CMP) is a group of blood tests that gives a broad look at your internal health, including your liver function, kidney function, blood sugar, and electrolyte levels.

In someone experiencing new depressive symptoms, a CMP can test for various medical conditions that may cause or contribute to symptoms that overlap with depression, including electrolyte abnormalities, glucose dysregulation (like hypoglycemia, which is low blood sugar), and kidney or liver disease. Because some psychiatric medications can affect these systems, a CMP may also provide useful baseline information when considering certain treatments.

Similar to a thyroid panel and CBC, a CMP is typically obtained during an annual physical. Although a CMP isn’t required to diagnose depression, it’s helpful to give your mental health provider the most recent results you have. If you don’t have a recent one, routine CMP testing may not be required but may be done if medical history, physical exam findings, or treatment planning indicate it.

4. Vitamins

Vitamin D and vitamin B12 deficiencies have both been associated with depressive symptoms. Although medical professionals are not completely certain of the link between vitamin D and depression, it makes sense that vitamin D levels could contribute to depression. That’s because there are vitamin D receptors in areas of the brain that regulate mood, and vitamin D plays a role in regulating serotonin.

Similarly, it makes sense that vitamin B12 can contribute to depressive symptoms because it helps support healthy nerve function and the production of brain chemicals that can impact mood. Additionally, B12 is necessary for healthy blood cells, and as previously mentioned, anemia can also lead to depressive symptoms.

On top of evidence that vitamin D and vitamin B12 deficiencies could lead to depressive symptoms, research shows that vitamin B and vitamin D supplementation can be an effective add-on therapy for depression, depending on an individual’s vitamin levels.

Although there are no guidelines suggesting that vitamin B12 or vitamin D need to be tested prior to diagnosing depression, depending on the other symptoms an individual is experiencing, as well as their health history, testing for these vitamin levels may be helpful. These labs are often obtained during physical exams and should be given to your mental health provider. Seeing these labs can help mental health providers further understand all of the potential contributing factors to depression, as well as know if future supplementation should be part of the treatment plan.

5. Drug Testing

Alcohol, drugs, and medications can contribute to or even cause depressive symptoms. Although blood alcohol level and drug tests are especially completed in offices and emergency departments when depressive symptoms come on suddenly, clinicians always ask about alcohol and drug use when someone comes in with depressive symptoms because depressive symptoms can be substance induced. Making this distinction is important because it means treating the substance use will be an essential part of treating the mood symptoms.

A number of commonly used medications — like corticosteroids (anti-inflammatory medications), oral contraceptives, isotretinoin (for acne), glucagon-like peptide-1 receptor agonists (GLP-1 RAs), and antiseizure medications — can contribute to depression. You typically don’t need to test for the level of most of these drugs, but letting your mental health provider know about all the medications you take can help them know if a drug may be contributing to your depression.

Important: The views and opinions expressed in this article are those of the author and not Everyday Health.

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Resources
  1. Lam RW et al. Canadian Network for Mood and Anxiety Treatments (CANMAT) 2023 Update on Clinical Guidelines for Management of Major Depressive Disorder in Adults. The Canadian Journal of Psychiatry. May 6, 2024.
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  3. Understanding the Link Between Chronic Disease and Depression. National Institute of Mental Health. 2024.
  4. Gupta B et al. Association of Anaemia and Depression: A Systematic Review and Meta-analysis. The Nigerian Medical Journal. November 2025.
  5. Comprehensive Metabolic Panel (CMP). MedlinePlus. December 4, 2023.
  6. Garicia-Altieri M et al. Management of depression/anxiety in patients with chronic liver disease. Clinical Liver Disease. June 2024.
  7. Karim S et al. Association Between Low Vitamin D Levels and Depression: A Systematic Review and Meta-Analysis. Cureus. May 2026.
  8. Kennedy KP et al. Vitamin B12 Supplementation in Psychiatric Practice. Current Psychiatry Reports. June 2024.
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Dr. Allison Young

Allison Young, MD

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Member of American College of Lifestyle Medicine

Allison Young, MD, is a board-certified psychiatrist providing services via telehealth throughout New York and Florida.

In addition to her private practice, Dr. Young serves as an a...

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