Skip to content
Blood Test Tracker

Selenium

Measures the trace mineral selenium in your blood, which mostly reflects how much you have recently taken in from food and supplements.

AI-verified against cited sources. Awaiting expert reviewAlso called SeLOINC 5724-0

Check your result

Sex (optional)

Type your result to see where it falls.

Nothing you type here leaves your browser.

What it is

Selenium is a trace mineral your body needs in tiny amounts. It is built into proteins that protect cells from damage and play a part in how the thyroid handles its hormones. Seafood, meat, poultry and Brazil nuts are rich sources, and the selenium in plant foods depends on the soil where they grew. A blood test mainly shows your recent intake.

Why it matters

Severe, long-lasting selenium shortage can contribute to heart muscle problems and can add to the effects of low iodine on the thyroid. Too much, usually from supplements, can cause hair and nail loss, stomach upset and nervous system symptoms. Deficiency is uncommon in the US and is mostly seen with long-term intravenous feeding or severe poor absorption, so this test is mostly used to follow supplementation rather than as a routine check.

If it’s low

A low result means you may not be getting enough selenium from food, or your body is not absorbing it well. A mild shortfall usually causes no symptoms. Severe, long-lasting deficiency is rare but can affect the heart muscle, and it can add to the effects of low iodine on the thyroid.

Common causes

  • A diet low in selenium, including a diet based on foods grown in low-selenium soil
  • Long-term intravenous or tube feeding without added selenium
  • Bowel surgery or digestive conditions that reduce absorption, such as Crohn's disease

What can help

  • Talk with a clinician about the likely cause and whether a supplement is right for you
  • Eat selenium-rich foods such as seafood, meat, poultry and eggs; Brazil nuts are very rich, so a little goes a long way
  • Ask whether and when to recheck the level

If it’s high

A high result most often comes from selenium supplements or a multivitamin. Very high levels over time can cause selenosis, with hair loss, brittle nails, a garlic smell on the breath, stomach upset and nervous system symptoms. A surprisingly high result can also come from contamination of the sample.

Common causes

  • High-dose selenium or multivitamin supplements
  • Eating Brazil nuts often, since they are very high in selenium
  • Eating food grown in selenium-rich soil
  • Contamination from a collection tube that was not trace-element-free

What can help

  • Review all your supplements and their selenium content with a clinician
  • Ask whether the test should be repeated in a certified trace-element-free tube if the result is unexpected

Usual ranges

What labs print as the reference range, by who was tested. Ranges differ a little between labs, so the range on your own report is the one your result is judged against.

The usual range depends on age. Choose an age to see the one that applies.

Children and teens 5 ranges

See Selenium by age and sex, with the U.S. survey numbers where they exist.

How common is your level?

NHANES describes the US civilian, non-institutionalized population, not a 'healthy' reference group. People with disease, on medication, fasting or not (except fasting-subsample markers), smokers and so on are all included. A percentile says where a value sits among Americans of that sex and age, not whether it is normal.

How Selenium varies with age in the U.S.Shaded: middle 90% and middle 50% of people. Line: the median. µg/L. Point at any age, or focus the chart and use the arrow keys, to read both sexes in words.

Use the left and right arrow keys to read each age. Shift moves five years.

Reference data derived from CDC/NCHS National Health and Nutrition Examination Survey (NHANES), cycles 2015-2016. Analysis by bloodtesttracker.com; not endorsed by CDC, NCHS or HHS.

Explore Selenium by age and sex: every percentile as a table, with a download.

What can affect your result

  • Recent intake from food and supplements
  • Where your food was grown, because soil selenium differs by region
  • Inflammation or acute illness
  • Age: infants and children have lower usual ranges than adults
  • Specimen type: serum or plasma holds about 75% of the selenium found in whole blood, so results from different specimen types are not interchangeable
  • Recent contrast dye for an imaging scan
  • Contrast dye containing gadolinium, iodine or barium can interfere with the metal-testing method; Mayo Clinic Laboratories advises waiting 96 hours after contrast before collecting the sample.
  • Vitamin and mineral supplements, including multivitamins, raise the result; ARUP suggests stopping nonessential supplements before the draw, if your clinician agrees.
  • Selenium is easy to contaminate. A tube that is not certified trace-element-free, or skin contamination, can falsely raise a result.
  • Inflammation and acute illness can affect the selenium-carrying proteins in blood, so a single result during illness may not reflect your usual status.

Serum selenium reflects recent intake, so it can shift as your diet or supplement use changes. Hair and nails reflect longer-term intake, over months to years.

When to talk to a clinician

Talk with a clinician if your result is below about 40 µg/L, the level where Mayo Clinic Laboratories says deficiency is usually seen. If you take selenium supplements and notice hair loss, brittle or blotchy nails, a garlic smell on your breath, nausea or nervous system symptoms, tell your clinician about the supplement.

Questions you could ask

  • Is serum selenium the right test for my situation, or would a different specimen be better?
  • Could my supplements or multivitamin be adding to this result?
  • Should we repeat the test in a trace-element-free tube to be sure?
  • Could my diet or a digestive condition explain this level?
  • Should we recheck it after a few months, and is a supplement worth discussing?

Questions people ask

Why do labs list such different normal ranges for selenium?

Labs use different methods and different reference groups. Mayo Clinic Laboratories lists 110 to 165 µg/L for adults, ARUP lists 23 to 190 µg/L, and the NIH says 80 µg/L or higher is usually enough. Compare your result with the range printed on your own report.

Is serum selenium the same as whole-blood selenium?

No. Serum or plasma contains about three quarters of the selenium in whole blood, so the numbers and ranges differ. Check which specimen your test used before comparing results.

How do I convert µg/L to µmol/L?

Multiply µg/L by 0.01266. For example, 120 µg/L is about 1.52 µmol/L. To go the other way, multiply µmol/L by 78.97.

Show the science and sources

Units

  • 1 µg/L = 1 µg/L
  • 1 µg/L = 0.01266 µmol/L
  • 1 µg/L = 0.1 µg/dL

Open the Selenium unit converter

Is a change real?

Selenium naturally varies about 7.8% from test to test in the same healthy person. Between two results from the same lab, a change of roughly 24% or more is unlikely to be day-to-day noise or lab variation (95% reference change value). Source: Systematic review and meta-analysis of within-subject and between-subject biological variation estimates of serum zinc, copper and selenium (Coskun A et al.).

For clinicians and researchers

Serum or plasma selenium reflects recent dietary intake and holds about 75% of whole-blood selenium (ARUP); hair and nail selenium reflect intake over months to years, and selenoproteins GPx3 and selenoprotein P are functional markers that inflammation can distort (NIH ODS). Mayo Clinic Laboratories (ICP-MS/MS) and ARUP (ICP-MS) both use mass spectrometry; trace-element-free collection tubes are needed, and gadolinium, iodine or barium contrast can interfere with ICP-MS metal tests (Mayo: wait 96 hours). Intervals vary: Mayo adult 110 to 165 µg/L, ARUP 23.0 to 190.0 µg/L, and NIH ODS treats 80 µg/L or more as usually sufficient. Mayo notes that in deficiency with loss of glutathione peroxidase activity, serum selenium is usually below 40 µg/L. Plasma and serum selenium is not interchangeable with whole-blood or red-cell selenium. The NIH tolerable upper intake level for adults is 400 µg/day from all sources.

LOINC 5724-0 (primary), 25521-6. Specimen: serum-or-plasma.

Sources

  1. Selenium, Serum (test SES), Mayo Clinic Laboratories
  2. Selenium, Serum or Plasma (test 0025023), ARUP Laboratories
  3. Selenium: Fact Sheet for Health Professionals, NIH Office of Dietary Supplements
  4. Selenium (compound summary, molecular weight), PubChem, National Library of Medicine

AI-verified against cited sources. Awaiting expert review. Last reviewed 2026-10-03. How we build and check these pages.

Related markers