Selenium deficiency testing is most useful for people whose health or diet makes low selenium more likely, such as those receiving long-term nutrition through a vein, people on dialysis, and people with conditions that reduce nutrient absorption. A clinician may also consider testing when ongoing symptoms occur alongside these risks. Most people eating a varied diet do not need routine testing because selenium deficiency is uncommon.
Who is more likely to need a selenium deficiency test?
Selenium is a mineral that the body needs in small amounts to support normal thyroid function, antioxidant activity, and other essential processes. Deficiency is uncommon in many populations, so testing is generally guided by a person's medical history, dietary intake, and possible signs of poor nutrition. The Merck Manual's patient guidance on selenium deficiency explains that clinicians assess a person's circumstances and symptoms when considering whether a deficiency may be present.
Testing may be worth discussing with a healthcare professional if one or more of the following circumstances applies:
- Long-term nutrition through a vein: People receiving total parenteral nutrition (TPN), which supplies nutrients directly into the bloodstream, may develop selenium deficiency, particularly when their nutritional needs are not adequately met.
- Long-term kidney dialysis: People receiving hemodialysis may have lower selenium levels. Dietary restrictions, reduced food intake, and selenium removal during dialysis can contribute to the risk.
- Digestive conditions that affect nutrient absorption: People with certain gastrointestinal disorders may not absorb nutrients normally. The likelihood of selenium deficiency depends on the specific condition and its effects on nutrition.
- Very limited or inadequate food intake: People with prolonged poor nutrition or highly restricted diets may need an assessment of their overall nutrient status, including selenium when appropriate.
- Living in a region with very low selenium levels in food: In some areas, soil contains little selenium, which can result in low selenium levels in locally grown foods. People whose diets depend heavily on these foods may have a greater risk of inadequate intake.
- Living with HIV: Some people with HIV have low selenium concentrations, which may be related to inadequate intake or problems with absorption. A clinician can determine whether testing is appropriate based on the person's nutritional and medical circumstances.
The National Institutes of Health Office of Dietary Supplements identifies people undergoing dialysis, people living with HIV, and people in selenium-deficient regions as groups at increased risk of inadequate selenium intake. These risk factors do not mean that everyone in these groups has a deficiency; they help clinicians decide when a closer nutritional assessment may be useful.
Can digestive problems increase the need for testing?
Yes. Certain gastrointestinal conditions can interfere with the body's ability to absorb nutrients from food. For example, MedlinePlus notes that severe gastrointestinal disorders, including Crohn's disease, may affect selenium absorption. Testing may be considered when a digestive disorder is accompanied by evidence of poor nutrition, persistent symptoms, or other reasons to suspect a nutrient deficiency. The need for testing depends on the condition, its severity, and the person's overall nutritional status.
Which symptoms may prompt a clinician to consider testing?
Selenium deficiency does not always cause obvious symptoms, and the symptoms that do occur can overlap with many other health problems. Muscle pain and tenderness have been reported in people who develop deficiency during prolonged intravenous feeding. Selenium deficiency may also contribute to thyroid problems when iodine intake is inadequate. However, muscle discomfort, fatigue, or thyroid symptoms alone are not specific enough to establish a selenium deficiency.
A clinician may consider selenium testing when such symptoms occur alongside a relevant risk factor, such as long-term intravenous nutrition, a condition affecting nutrient absorption, or significant dietary inadequacy. Persistent or worsening symptoms should be assessed more broadly because other nutritional deficiencies, medical conditions, and medication effects may produce similar experiences.
Do vegetarians, vegans, or people with thyroid problems need testing?
Not necessarily. People following vegetarian or vegan diets may have lower selenium intake depending on their food choices and the selenium content of foods available in their region. However, following a plant-based diet does not automatically mean that someone is deficient or needs a blood test. A clinician may review food intake and consider testing if the diet is particularly limited or additional risk factors are present.
Thyroid disease by itself is also not proof of selenium deficiency. Selenium and iodine both have roles in thyroid health, and deficiencies in both nutrients can contribute to certain thyroid problems. Testing may be appropriate in selected situations, especially when there are additional nutritional concerns, but selenium testing is not a substitute for the usual evaluation of thyroid function.
How do doctors test for selenium deficiency?
When testing is considered appropriate, a healthcare professional may request a blood test measuring selenium in serum or plasma. These are commonly used measures of selenium status. The National Institutes of Health Office of Dietary Supplements explains that these measurements can reflect recent selenium intake, while other markers used to assess selenium status may be affected by inflammation. Results therefore need to be interpreted alongside the person's medical history, dietary intake, and clinical findings.
Testing availability varies by location. According to the Merck Manual Professional Edition, clinicians may assess suspected selenium deficiency through the patient's history and physical examination and sometimes through plasma selenium measurements or tests of glutathione peroxidase activity. These specialized tests are not readily available in all settings.
A healthcare professional may also review other investigations when symptoms suggest a broader nutritional problem. For example, thyroid function tests may be appropriate when thyroid symptoms are present. The choice of tests depends on the clinical concern; there is no single symptom or test result that should be interpreted without context.
Who usually does not need routine selenium testing?
Most otherwise healthy people who eat a varied diet and have no relevant medical or nutritional risk factors do not need selenium testing simply to check their nutrient levels. Selenium deficiency is uncommon in many countries, and general symptoms such as tiredness or muscle aches do not automatically point to a deficiency.
Likewise, taking supplements without evidence of a need is not a reliable way to determine selenium status. Selenium is essential, but excessive intake can be harmful. People who are concerned about their diet or have ongoing health problems should discuss their nutritional needs with a healthcare professional before starting high-dose selenium supplements.
What should you discuss with your healthcare professional?
If you think testing might be appropriate, explain any persistent symptoms, digestive conditions, dialysis treatment, long-term intravenous nutrition, changes in appetite, or dietary restrictions. Mention any vitamin or mineral supplements you already take, including the selenium content if it is listed on the label. This information helps the clinician decide whether selenium testing is useful or whether another investigation would better explain the concern.
The main consideration is whether your personal circumstances make low selenium sufficiently likely to warrant testing. A targeted assessment can help identify nutritional concerns without relying on symptoms alone or ordering unnecessary tests.