Can Depression Be Detected With a Blood Test?

technician holding blood sample in test tube
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Although promising research has been done into potential markers for depression, there is not yet a blood test which can be used to definitively identify people who are suffering from depression. Instead, your doctor uses your reported symptoms, the signs he observes during your office visit, your medical history, and your family's medical history to make his diagnosis.

When you first visit your physician, however, you may be given certain blood tests to rule out medical illnesses which may either cause depression or have similar symptoms.

Blood Tests You Might Be Given If You Have Depression Symptoms

  • Complete Blood Count (CBC): A CBC is a test which analyzes the numbers of various types of cells found in blood. It looks for anemia or infection, both of which may cause symptoms similar to depression, such as lethargy and fatigue.
  • Thyroid Function Check: This test measures the blood levels of the various hormones produced by the thyroid gland. When the thyroid gland is either over- or underactive, it can contribute to a mood disorder.
  • Creatinine and Blood Urea Nitrogen (BUN): These two tests measure different aspects of kidney function. They are tested because kidney disease can lead to symptoms similar to depression. It is also important to know if there is any impairment in kidney function because this can influence how depression medications are metabolized.
  • Liver Function Check: This test measures levels of various enzymes produced by the liver, which may be elevated when the liver is inflamed or damaged. Liver disease can cause symptoms similar to depression, such as fatigue and lethargy. In addition, the poor liver function can indicate alcohol abuse, which itself may depress mood. It is also important to know if there is any impairment in liver function because this can influence how medications for depression are metabolized.
  • Fasting Blood Glucose: This test measures how much sugar is in the blood after an overnight fast and is used to detect diabetes. While the exact link between depression and diabetes is unclear, the two often go hand-in-hand and some studies seem to indicate that those with diabetes are at a greater risk of developing depression. This test may also be necessary before certain psychiatric medications are prescribed.
  • Cholesterol: This test provides a rough measure of the amount of cholesterol in your blood. Too much cholesterol is associated with clogged arteries and heart disease. Cholesterol is not specifically linked to depression, but its levels indicate your general health. In addition, cholesterol testing may be necessary prior to prescribing certain psychiatric medications.
  • Calcium and Magnesium Levels: These tests detect the amount of calcium and magnesium in the blood. High or low calcium or magnesium levels are a rare cause of psychiatric illness.
  • Folic Acid and Vitamin B12 Levels: These tests measure the blood levels of these two vitamins. Low levels of either folic acid or vitamin B12 are associated with pernicious anemia, which may cause symptoms of depression and lethargy, even before any other deficiency symptoms show up.
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    Article Sources

    • Ferri, Fred F. Ferri's Clinical Advisor 2009. 1st ed. Philadelphia: Mobsy, 2009.