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This article waslast modified on 13 June 2023.
At a Glance
Why Get Tested?

To measure the amount of selenium in the blood in order to identify/diagnose deficiency/toxicity or to monitor the response to supplementation

When To Get Tested?

When you have symptoms that may suggest selenium deficiency or toxicity. Following guidelines for the screening of malnutrition or if at risk of malnutrition.

Sample Required?

A blood sample taken from a vein in your arm.

Test Preparation Needed?


On average it takes 7 working days for the blood test results to come back from the hospital, depending on the exact tests requested. Some specialist test results may take longer, if samples have to be sent to a reference (specialist) laboratory. The X-ray & scan results may take longer. If you are registered to use the online services of your local practice, you may be able to access your results online. Your GP practice will be able to provide specific details.

If the doctor wants to see you about the result(s), you will be offered an appointment. If you are concerned about your test results, you will need to arrange an appointment with your doctor so that all relevant information including age, ethnicity, health history, signs and symptoms, laboratory and other procedures (radiology, endoscopy, etc.), can be considered.

Lab Tests Online-UK is an educational website designed to provide patients and carers with information on laboratory tests used in medical care. We are not a laboratory and are unable to comment on an individual's health and treatment.

Reference ranges are dependent on many factors, including patient age, sex, sample population, and test method, and numeric test results can have different meanings in different laboratories.

For these reasons, you will not find reference ranges for the majority of tests described on this web site. The lab report containing your test results should include the relevant reference range for your test(s). Please consult your doctor or the laboratory that performed the test(s) to obtain the reference range if you do not have the lab report.

For more information on reference ranges, please read Reference Ranges and What They Mean.

What is being tested?

This test measures the amount of selenium in the blood. Selenium is an essential trace element with important functions throughout the body. Selenium has several important roles including the synthesis and metabolism of thyroid hormones, immune function and in antioxidative processes.

Selenium is found in many foods but has highest quantities in brazil nuts, seafood, kidney and meat.

The selenium content of rice and cereals varies depending upon the geographical region as some soils are high in selenium (USA) whereas others have low levels (New Zealand). Selenium is well absorbed from the gastrointestinal tract and homeostasis is achieved by excretion in the urine.

If selenium deficiency is severe it can present clinically with muscle weakness, dizziness, nausea and cardiomyopathy. Toxicity may also occur following over-ingestion of supplements/foods or through occupational exposure e.g manufacturing processes such as ceramics, glass and semiconductors. Symptoms of toxicity include irritation to eyes and mucus membranes, hair and nail changes, discolouration of teeth, altered consciousness and cardio-respiratory arrest.

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Common Questions
  • How is it used?

    Selenium testing is used to investigate for selenium deficiency or rarely to investigate for selenium toxicity. Selenium is often measured along with other trace elements (e.g iron, zinc & copper) to identify deficiencies where a person may benefit from supplementation.

  • When is it requested?

    When a person has suspected selenium deficiency or toxicity. In particular selenium is measured in individuals receiving supplements, especially those who are receiving total parenteral nutrition (TPN) which is supplemented via the non-oral route.

  • What does the test result mean?

    Serum/plasma selenium concentrations can decrease during an acute illness or trauma. This does not necessarily infer selenium deficiency but may be a response to a redistribution of selenium (into tissues). Whole blood selenium measurements are not effected by acute illness and can be a more reliable marker. Serum/plasma selenium concentrations correspond to recent selenium intake whereas the measurement of whole blood selenium correlates with longer-term (roughly 2 months) selenium status.

  • Is there anything else I should know?

    Low selenium intake and deficiency has been associated with increased risk of cancer and cardiomyopathy. Supplementation may improve brain function in particular it is thought to improve mood, depression, anxiety and confusion.

  • Should I take selenium supplements?

    Most individuals have an adequate supply of selenium in their diet and supplementation is not necessary. However, if you have any concerns please consult your GP who can review your dietary intake, investigate any symptoms and advise if testing is required.

  • What is the difference between plasma selenium and red cell selenium?

    Plasma selenium is a marker of immediate selenium status and varies daily depending upon dietary intake and any concurrent infections. Red cell selenium measures the selenium content inside red cells and gives an indication of total body selenium stores.