Selenium is an essential trace element incorporated into proteins called selenoproteins. These selenoproteins have diverse functions, including regulating thyroid hormone metabolism and supporting the body’s antioxidant defense system. Testing selenium levels directly evaluates an individual’s nutritional status, helping healthcare providers identify potential deficiencies or toxic overexposure and determine if intake is adequate for optimal health.
Reasons for Measuring Selenium Status
A healthcare provider requests a selenium test when a patient shows signs of extreme imbalance. Indications of possible deficiency include muscle pain, weakness, compromised immune function, or cardiomyopathy (historically known as Keshan disease). Since selenium is integral to thyroid function, testing may also be prompted when thyroid disorders are present.
Conversely, symptoms of potential overexposure, or selenosis, also trigger a test request. These signs often manifest as changes to the hair and nails, such as brittleness, loss, or discoloration, along with gastrointestinal distress. Testing is routinely performed for individuals receiving total parenteral nutrition (TPN) without selenium supplementation. People living in geographical areas known to have very low or very high soil selenium content may also be monitored.
Analyzing Biological Samples
Assessing selenium status most commonly involves analyzing blood samples, where the specific sample type is important for interpretation. Measuring selenium in serum or plasma (the fluid component of blood) primarily reflects recent dietary intake and short-term status over preceding weeks. The concentration of selenoprotein P (SePP), the main selenium-carrying protein, is often measured alongside total selenium to provide a more functional assessment.
Whole blood testing, which includes the selenium contained within red blood cells, is considered a better indicator of long-term selenium status, reflecting intake over several months. Another method is the functional measurement of the enzyme glutathione peroxidase (GPx) activity, as this enzyme is selenium-dependent. However, GPx activity levels plateau once minimum selenium intake is reached, making it less reliable for detecting high or toxic levels.
Urine samples are collected and analyzed to monitor recent selenium intake and excretion, making them useful for assessing acute or occupational exposure. Because excretion can be highly variable day-to-day, a single urine test is less reliable for determining long-term nutritional state. Other tissues, such as hair or nail clippings, reflect exposure over many months, but these samples are reserved for epidemiological research due to their variability in a clinical setting.
Interpreting Test Results
Interpreting selenium test results involves comparing the measured concentration to established reference ranges, which may vary slightly between laboratories. A result falling into the adequate range suggests the body has sufficient selenium stores to support selenoprotein function. For serum selenium, the adequate range for adults is typically 70 to 160 micrograms per liter (µg/L).
A result below the lower limit indicates a selenium deficiency, meaning the body may not be able to synthesize enough functional selenoproteins. Clinically confirmed deficiency requires nutritional intervention, usually supplementation, to restore levels and prevent associated health issues like myopathy or cardiac dysfunction. The specific test utilized must be considered, as low serum selenium reflects recent poor intake, while low whole blood levels suggest chronic depletion.
Conversely, results significantly above the upper reference limit indicate excessive intake and potential toxicity, known as selenosis. Chronic toxicity is associated with sustained high exposure. Clinical management focuses on identifying and eliminating the source of excess selenium, such as contaminated water or high-dose supplements. Ultimately, the test result must be combined with the patient’s physical symptoms and dietary history for a meaningful clinical diagnosis.