Vitamins and nutrition . Patient guide
Selenium Blood Test
What is Selenium
Selenium is a trace mineral essential for thyroid hormone metabolism, antioxidant defence (glutathione peroxidase), and immune function. UK soil is naturally low in selenium so dietary intake is lower than in many other countries, making selenium status a clinically relevant marker.
This biomarker entry is being clinically reviewed by our team. The factual content draws on UK guidance (NICE, NHS, Royal Colleges and the relevant speciality society where cited).
Reference range
Reported in µmol/L (also seen as µg/L (multiply µmol/L by 79)). Final reports always carry the issuing laboratory's range, which is what your clinician will interpret against.
| Group | Range | Note |
|---|---|---|
| Adequate (UK adults) | 0.89 to 1.65 | µmol/L |
| Borderline / deficient | 0.70 to 0.89 | |
| Deficient | under 0.70 | |
| Excess (review supplementation) | over 1.90 |
What it is
Selenium is incorporated into selenoproteins, including the deiodinase enzymes that convert thyroxine (T4) into the active hormone triiodothyronine (T3), and into glutathione peroxidase, a key antioxidant. UK food sources include Brazil nuts (by far the highest), seafood, organ meats, and eggs.
Why a clinician would order it
Selenium is checked in autoimmune thyroid disease (particularly Hashimoto's, where adequate selenium reduces TPO antibody levels in some studies), in unexplained fatigue or low immunity, in patients with restricted diets, and as part of comprehensive wellness screening. Particularly relevant in patients investigating thyroid hair loss.
If your level is outside the range
Symptoms of low Selenium
- Fatigue
- Hair loss
- Frequent infections
- Brittle nails
- Possible worsening of autoimmune thyroid disease
What low can indicate. Inadequate dietary intake (UK diet without Brazil nuts or organ meats often runs marginal), malabsorption, restrictive eating, or increased demand in autoimmune thyroid disease.
Symptoms of high Selenium
- Garlic-like breath
- Brittle nails or nail loss
- Hair loss (paradoxically - high selenium can also cause hair shedding)
- Skin rash
- Nausea, fatigue
What high can indicate. Excessive Brazil nut intake (selenium content per nut typically 70 to 90 micrograms but highly variable, and the NHS guidance for supplemental selenium is up to 350 micrograms daily), or over-supplementation.
Testing tips
No fasting required. Hold selenium supplements for at least 48 hours before testing. Note Brazil nut intake when discussing results. Selenium is one of the few nutrients where excess can mimic deficiency in causing hair loss, so supplementation should be guided by a measured baseline.
Where you can get this tested
Selenium is not part of a standard WMG Health panel, but it can be added to one. Build a custom panel and our clinicians will confirm the markers and price in writing before you book.
Looking to book a test?
Comprehensive private health screening
Full blood screening at 134 Harley Street, London, reviewed by GMC-registered doctors with a written interpretation.
Sources
UK guidance our clinicians use when interpreting this marker.
This page is general patient information, not personal medical advice. A GMC-registered clinician will review your results and tailor any interpretation to you. See our Editorial Policy for how we write and review content.
Common questions about Selenium
What is a normal Selenium range?
Adequate (UK adults): 0.89 to 1.65 (µmol/L). Borderline / deficient: 0.70 to 0.89. Deficient: under 0.70. Excess (review supplementation): over 1.90. Always interpret your own results against the laboratory range printed on your report, since assay-specific reference ranges vary.
What does a low Selenium result mean?
Inadequate dietary intake (UK diet without Brazil nuts or organ meats often runs marginal), malabsorption, restrictive eating, or increased demand in autoimmune thyroid disease.
What does a high Selenium result mean?
Excessive Brazil nut intake (selenium content per nut typically 70 to 90 micrograms but highly variable, and the NHS guidance for supplemental selenium is up to 350 micrograms daily), or over-supplementation.
Do I need to fast or prepare for the Selenium blood test?
No fasting required. Hold selenium supplements for at least 48 hours before testing. Note Brazil nut intake when discussing results. Selenium is one of the few nutrients where excess can mimic deficiency in causing hair loss, so supplementation should be guided by a measured baseline.
Can I order a Selenium blood test privately in London?
Yes. WMG Health offers Selenium as part of a custom panel at our 134 Harley Street clinic. Results are released as each marker is reviewed, and the completion date is set by the slowest marker in your panel. We confirm the expected timeframe at booking. Book a standard panel online, or ask for a custom panel via /contact/ or 020 3239 3378.