The Selenium test is a blood test that measures the level of selenium, an essential trace mineral that the body cannot produce on its own and must obtain entirely from dietary sources including Brazil nuts, seafood, meat, eggs, and certain grains. Selenium functions as a critical component of selenoproteins, a family of proteins with diverse and essential roles in antioxidant defence, thyroid hormone metabolism, immune function, DNA synthesis, and reproductive health. The most important selenoproteins include glutathione peroxidase, which protects cells from oxidative damage, and iodothyronine deiodinase, which converts the inactive thyroid hormone T4 into the biologically active T3.
Selenium deficiency, while less widely recognised than iron or Vitamin D deficiency in India, is an increasingly documented nutritional problem particularly in regions with selenium-depleted soils, among vegetarians with limited dietary diversity, and in patients with chronic gastrointestinal malabsorption conditions. Deficiency is associated with thyroid dysfunction, impaired immune response, increased susceptibility to viral infections, male infertility, and in severe cases Keshan disease, a cardiomyopathy caused by extreme selenium depletion first described in selenium-deficient regions of China but relevant wherever soil selenium is low. Conversely, excessive selenium intake from supplements causes selenosis, a toxicity syndrome with characteristic symptoms. The test involves a simple blood draw completed in under five minutes.
