What this test measures
Serum selenium reflects recent intake (last few weeks). Selenium is incorporated into selenoproteins including glutathione peroxidase (antioxidant), thioredoxin reductase, and the iodothyronine deiodinases (T4 → T3 conversion). Whole-blood selenium reflects longer-term status; toenail selenium reflects intake over the past 6–12 months. Most clinical questions use serum or plasma.
Why it matters
Indian selenium status varies geographically — soil selenium in the Indo-Gangetic plain is generally adequate but parts of north-east India and a few pockets are low. Frank deficiency (causing Keshan cardiomyopathy or Kashin-Beck osteoarthropathy as seen in parts of China) is rare in India. Mild insufficiency may contribute to autoimmune thyroid disease and iodine misutilisation. Acute toxicity ("selenosis") from over-supplementation causes garlic breath, hair and nail brittleness, fatigue, and peripheral neuropathy — most cases trace to mislabelled supplements.
How to prepare
Fast 4–8 hours preferred; collect a morning serum sample in a trace-metal-free royal-blue-top tube. Stop selenium supplements (often 100–200 µg/day in multivitamins) for 48 hours unless monitoring therapeutic levels.
Markers & reference ranges
Reference ranges below are typical adult values. Your lab's reported range may differ slightly based on the assay platform and patient demographics — always read your report against the range printed on it.
| Marker | Normal range | If low | If high |
|---|---|---|---|
| Serum Selenium (µg/L)[1][2] | Adults 70 – 150 | < 70 µg/L: insufficient — typically from low dietary intake (low-Se regions, parenteral nutrition without selenium, malabsorption), or replenishment failure (advanced liver disease). May contribute to autoimmune thyroid disease, increased oxidative stress. Replace via diet (Brazil nuts — 1–2 nuts/day = full RDA) or supplement 50–100 µg/day; re-test 3 months. | > 200 µg/L: excess — almost always from supplements. > 400 µg/L: selenosis risk (hair and nail loss, garlic breath, GI upset, peripheral neuropathy). Stop supplements; serum normalises in weeks. Brazil nut over-consumption (some nuts contain 50–100 µg each) is a documented cause. |
Serum selenium bands
| Selenium (µg/L) | Status | Action |
|---|---|---|
| < 45 | Deficient | Investigate cause; replace via diet or 100 µg supplement |
| 45 – 69 | Insufficient | Dietary review; consider 50 µg supplement |
| 70 – 150 | Adequate | No action |
| 151 – 400 | High — supplementation | Review supplement dose; reduce |
| > 400 | Toxic (selenosis) | Stop selenium intake immediately; symptomatic care |
Frequently asked questions
Should I take selenium for my thyroid?
Modest evidence in autoimmune thyroiditis: 200 µg/day for 3–6 months may slightly lower TPO antibody titres in some studies. Effects on clinical outcomes (progression to hypothyroidism) are not clearly established. Don't exceed 200 µg/day chronically — chronic over-intake is harmful.
Are Brazil nuts a good source?
Very good — 1–2 nuts/day usually meet the 55 µg adult RDA. But selenium content varies hugely by region of origin (some contain 50 µg per nut, others 200+). Eating 6+ nuts/day for months has caused selenosis.
How do I tell if my hair loss is from selenium?
Hair / nail brittleness from selenium toxicity is usually accompanied by garlic breath and chronic supplement intake — and the serum level is markedly elevated. Most hair loss has other causes (iron deficiency, thyroid disease, telogen effluvium).
Does selenium prevent cancer?
The SELECT trial showed no protective effect of selenium supplementation against prostate cancer in selenium-replete populations. Trials in selenium-deficient populations have shown mixed cancer outcomes. Routine selenium supplementation for cancer prevention is not recommended.
What's the upper safe limit?
UL for adults is 400 µg/day. Chronic intake above this risks selenosis. RDA is 55 µg adults; pregnancy 60 µg; lactation 70 µg.
Related Toxicology / Trace Elements tests
Tests commonly ordered alongside SELENIUM, or that help interpret an unexpected result.
Sources & references
- NIH ODS — Selenium Fact Sheet · accessed 2026-05-30T00:00:00.000Z
- Mayo Clinic Labs — Selenium, Serum · accessed 2026-05-30T00:00:00.000Z
- ATSDR — Toxicological Profile for Selenium · accessed 2026-05-30T00:00:00.000Z
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