Selenium

Selenium is an essential element that is a cofactor for glutathione peroxidase (GSH-Px). The normal daily dietary intake of selenium is 0.01 to 0.04 parts per million (ppm), which is similar to the typical content of soil (0.05 ppm) and sea water (0.09 ppm). Selenium is included in many over-the-counter vitamins because its antioxidant activity has been rumored to prevent cancer. 

Selenium deficiency leads to decreased GSH-Px activity, which is associated with cell membrane damage by free radicals. The most serious complication of selenium deficiency is painful muscle weakness and chronic congestive heart failure due to cardiomyopathy. Cardiac myocytes die and are replaced by fibrous tissue. Some patients may also exhibit macrocytosis, depigmentation of skin and hair, and elevated serum transaminase and creatine kinase levels.

In the United States, the most common cause of selenium deficiency is use of total parenteral nutrition for longer than one week. Patients are treated with selenium supplements to maintain the serum concentration above 70 ug/L. Selenium deficiency can also occur in people who are severely malnourished. 

Selenium toxicity may occur from industrial exposure drinking water in some regions of the world. Selenium is produced as a byproduct of copper refining and is used in electronic semiconductors, as a decolorizing agent for ceramics and glass, and as a vulcanizing agent in the rubber industry.

Toxic symptoms include garlic breath odor, thick brittle fingernails, dry brittle hair, red swollen skin of the hands and feet, and nervous system abnormalities of numbness, convulsions, or paralysis.

Selenium is measured in serum by inductively coupled plasma mass spectrometry (ICP-MS).  Blood should be collected in a royal blue-top tube that is free of trace elements. 

The reference ranges for serum selenium are age dependent. The reference range for adults is 110-165 ug/L. Glutathione peroxidase activity is usually inhibited when the serum concentration falls below 40 ug/L.

Specimen is whole blood collected into a royal blue-top (EDTA) Vacutainer tube, which is free of trace elements. High concentrations of gadolinium and iodine are known to interfere with the test of most metals. If either gadolinium- or iodine-containing contrast media has been administered, a specimen should not be collected for 96 hours.

References

Lalonde L, et al. Fluorometry of selenium in serum or urine. Clin Chem.1982; 28(1):172-174.

Muntau AC, et al. Age-related reference values for serum selenium concentrations in infants and children. Clin Chem. 2002;48(3):555-560.

Skelton JA, Havens PL, Werlin SL. Nutrient deficiencies in tube-fed children. Clin Pediatr. 2006;45(1):37-41.