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Selenium
An antioxidant trace element vital for the thyroid gland and immunity. Deficiency is possible in regions with poor soils.
Other names: Selenium, SeSection: Trace elementsSpecialist: Primary care physician, endocrinologistSample: Venous blood
Updated: September 17, 2026·MedProtect editorial team Reference information — not a diagnosis or a prescription
In shortNormal selenium in serum is 70–150 µg/L. Deficiency relates to thyroid function and immunity; excess (selenosis) — to uncontrolled supplement intake. The level depends on the region: most Russian soils are selenium-poor.
What this marker is
Selenium is part of antioxidant enzymes (glutathione peroxidase) and of the enzymes converting T4 into active T3 — so its deficiency hits the thyroid and immune defense.
The range between “normal” and “toxic” is narrow: above-normal supplements quickly cause selenosis (brittle nails and hair, garlic smell on breath, neuro symptoms). The test is a prerequisite before taking supplements.
Reference ranges
Group
Reference range
Adults
70–150 µg/L (0.9–1.9 µmol/L)
Children
below adults, rising with age; per the lab report
Brazil nuts can sharply raise the level: 1–2 nuts a day cover the daily norm. Tell the doctor about diet before testing and before supplements. Ranges differ between laboratories.
Check your value
Enter the number from your lab report — see how it compares with the typical range. Mind the units shown in the chosen row.
An approximate comparison with a typical range, not a diagnosis. Ranges differ between laboratories — use the one on your report; a doctor interprets the result.
Units and conversion
Measured in: µmol/L
µmol/L=µg/dL
µg/dL = µmol/L × 7.90 (selenium, molar mass 79.0)
When it is high or appears: possible causes
Selenosis from supplementsBrittle nails and hair, garlic smell, nausea, neurological symptoms.
Excess in dietMany Brazil nuts daily.
When it is low: possible causes
Selenium-poor soilsMost of Russia — selenium-deficient territory.
Impaired absorptionGI disease, long-term parenteral nutrition without supplements.
Increased needsThyroid disease, pregnancy.
What can skew the result
These factors can shift the result without any disease — keep them in mind before a retest:
Selenium supplementsBrazil nuts in dietGI diseaseVitamin E (synergy)
How to prepare
In the morning, fasting (8–12 hours), venous blood. Biotin (vitamin B7) in multivitamins can distort some immunoassays — tell the doctor about supplements. Details: Preparation: venous blood.
When a retest makes sense
Deficiency is confirmed by a repeat test in 2–4 weeks; monitoring during supplements is set by the doctor, usually at 8–12 weeks.
Who usually reviews this result
An out-of-range result is usually reviewed by: Primary care physician, endocrinologist. Bring your report and any previous results to the visit.
Names used on lab reports
Look for one of these names on your report: SeleniumSeleniumSelenium
Several markers on your report?
The app reads your whole report — this marker together with its neighbors, not one by one.
Selenium is needed by the enzymes converting T4 to active T3, and in autoimmune thyroiditis its deficiency worsens the course. But it is prescribed for a proven deficiency, not “for everyone with TSH problems”.
How to tell selenium is too high?
Selenosis: brittle and splitting nails, hair loss, garlic breath smell, nausea, irritability. Usually from supplements — stop them and monitor the level.
Should selenium be tested before supplements?
Yes, always: the corridor between normal and toxic is narrow, and in selenium-poor regions deficiency is common — the test answers whether a supplement is needed at all.
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