Selenium Blood Test
A selenium blood test measures the concentration of this vital trace element in your bloodstream. Selenium is a key component of selenoproteins -- enzymes that protect cells from oxidative damage and play a central role in thyroid hormone conversion. Low selenium can impair thyroid function even when TSH and T4 appear normal, making this test an important part of a comprehensive thyroid and metabolic assessment.
Why Test Selenium?
Testing selenium is valuable when evaluating thyroid health, particularly in hypothyroidism or Hashimoto's thyroiditis, where low selenium has been associated with higher TPO antibody levels. It is also useful for assessing antioxidant status in chronic inflammation or autoimmune disease, monitoring supplementation, and investigating unexplained fatigue, brain fog, or cold sensitivity.
What Do High Selenium Levels Mean?
Elevated selenium levels are rare and typically result from unsupervised supplementation. Sustained high levels can cause selenium toxicity (selenosis), with symptoms including gastrointestinal upset, hair loss, brittle nails, skin rashes, and nervous system effects such as peripheral neuropathy.
What Do Low Selenium Levels Mean?
Low selenium levels may indicate dietary deficiency, malabsorption (e.g. in inflammatory bowel disease), or increased oxidative stress. Insufficient selenium can impair the conversion of T4 to active T3, potentially leading to symptoms of thyroid dysfunction such as fatigue, brain fog, weight gain, and cold sensitivity -- even when standard thyroid tests look normal.
Symptoms to Watch For
- Fatigue and brain fog
- Cold sensitivity despite normal thyroid tests
- Unexplained weight gain
- Weakened immune response
- Hair loss or brittle nails
- Muscle weakness
- Reduced fertility
Who Should Get Tested?
- People with hypothyroidism or Hashimoto's thyroiditis
- Individuals with chronic inflammation or autoimmune disease
- Those experiencing fatigue, brain fog, or thyroid-related symptoms despite normal TSH
- People with inflammatory bowel disease or malabsorption conditions
- Anyone supplementing with selenium who wants to monitor levels
- Individuals on restricted diets low in selenium-rich foods
How to Prepare for Your Test
No special preparation is required for this test. Bring valid ID to your appointment.
Frequently Asked Questions
How does selenium relate to thyroid function?
What foods are rich in selenium?
Can too much selenium be dangerous?
Reviewed by
Wellth Team
Wellth
Our content is written and reviewed by Wellth, and fact-checked against peer-reviewed research and current Swedish clinical guidelines.
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The information on this page is provided for informational purposes only and does not constitute professional medical advice, diagnosis, or treatment. Wellth provides health information and testing services but is not a substitute for clinical care. Always consult a qualified healthcare provider if you have questions about a medical condition. If you are experiencing severe or urgent symptoms, contact your doctor or call 1177 Vårdguiden. Blood test results should be interpreted by a qualified healthcare professional in the context of your complete medical history.