|Values are valid only on day of printing.|
Selenium is an essential element. It is a cofactor required to maintain activity of glutathione peroxidase (GSH-Px), an enzyme that catalyzes the degradation of organic hydroperoxides. The absence of selenium correlates with loss of GSH-Px activity and is associated with damage to cell membranes due to accumulation of free radicals.
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 found in many over-the-counter vitamin preparations because its antioxidant activity is thought to be anticarcinogenic. There is no supporting evidence that selenium suppresses cancer.
In humans, cardiac muscle is the most susceptible to selenium deficiency. With cell membrane damage, normal cells are replaced by fibroblasts. This condition is known as cardiomyopathy and is characterized by an enlarged heart whose muscle is largely replaced by fibrous tissue.
In the United States, selenium deficiency is related to use of total parenteral nutrition. This is therapy administered to patients with no functional bowel, such as after surgical removal of the small and large intestine because of cancer, or because of acute inflammatory bowel disease such as Crohn's disease. Selenium supplementation to raise serum concentration >70 ng/mL is the usual treatment. Serum monitoring done on a semiannual basis checks the adequacy of supplementation.
Selenium toxicity has been observed in animals when daily intake exceeds 4 ppm. Teratogenic effects are frequently noted in the offspring of animals living in regions where soil content is high in selenium such as south-central South Dakota and northern-coastal regions of California. Selenium toxicity in humans is not known to be a significant problem except in acute overdose cases. Selenium is not classified as a human teratogen.
Monitoring selenium replacement therapy
Selenium accumulates in biological tissue. The normal concentration in adult human blood serum is 70 to 150 ng/mL (0.15 parts per million) with a population mean value of 98 ng/mL. Optimal selenium concentration is age dependent (see Reference Values); children require less circulating selenium than do adults.
In the state of selenium deficiency associated with loss of glutathione peroxidase activity, the serum concentration is usually <40 ng/mL.
Selenium is quite volatile; therefore, careful specimen collection is necessary to ensure accurate results.
High concentrations of gadolinium, iodine, and barium are known to interfere with most metals tests. If either gadolinium-, iodine-, or barium-containing contrast media has been administered, a specimen should not be collected for 96 hours.
0-2 months: 45-90 ng/mL
3-6 months: 50-120 ng/mL
7-9 months: 60-120 ng/mL
10-12 months: 70-130 ng/mL
>1 year: 70-150 ng/mL
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