Selenium, Whole Blood

The Selenium, Whole Blood test (also referred to as Selenium [Se], blood) is used to assess selenium deficiency and to monitor exposure or toxicity. It supports evaluation of people living in low-selenium regions, patients with malabsorption, individuals on long-term parenteral nutrition, and those following bariatric surgery. The measurement is additionally applicable in selected metabolic conditions such as propionic acidemia, in which trace element assessment may be part of longitudinal care. Because whole blood includes the erythrocyte compartment, it integrates short- and intermediate-term status and is suitable for follow-up when supplementation or exposure has changed.

Selenium is an essential micronutrient required for the biosynthesis of selenoproteins such as glutathione peroxidases and thioredoxin reductases, which limit oxidative damage and maintain cellular redox balance. It also supports thyroid hormone metabolism through the iodothyronine deiodinases and contributes to normal immune and reproductive function. Insufficient selenium intake or absorption can blunt antioxidant defense and immune responses and has been linked to cardiomyopathy characteristic of Keshan disease. Deficiency may also contribute to hypothyroidism with myxedema—particularly when iodine deficiency co-occurs—impair linear growth and neurocognitive development, and is implicated in the endemic osteoarthropathy Kashin–Beck disease. In contrast, excess exposure leads to selenosis, which can present with a garlic-like breath odor from dimethyl selenide, gastrointestinal complaints, hair loss, brittle nails, dermatitis, and peripheral neuropathy. Dietary intake is the primary source for most individuals and typically suffices with mixed diets. Risk for deficiency increases with poor intake, malabsorption, or extended parenteral nutrition lacking selenium supplementation. Whole-blood measurement reflects selenium within both erythrocytes and plasma, providing an integrated view of selenium status and recent exposure.