Detection in biological fluids
Selenium may be measured in blood, plasma, serum, or urine to monitor excessive environmental or occupational exposure, to confirm a diagnosis of poisoning in hospitalized victims, or investigate a suspected case of fatal overdose. Some analytical techniques are capable of distinguishing organic from inorganic forms of the element. Both organic and inorganic forms of selenium are largely converted to monosaccharide conjugates (selenosugars) in the body prior to elimination in the urine. Cancer patients receiving daily oral doses of selenothionine may achieve very high plasma and urine selenium concentrations. Toxicity
Although selenium is an essential trace element, it is toxic if taken in excess. Exceeding the Tolerable Upper Intake Level of 400 micrograms per day can lead to selenosis. This 400 µg Tolerable Upper Intake Level is based primarily on a 1986 study of five Chinese patients who exhibited overt signs of selenosis and a follow up study on the same five people in 1992. The 1992 study actually found the maximum safe dietary Se intake to be approximately 800 micrograms per day (15 micrograms per kilogram body weight), but suggested 400 micrograms per day to avoid creating an imbalance of nutrients in the diet and to accord with data from other countries. In China, people who ingested corn grown in extremely selenium-rich stony coal (carbonaceous shale) have suffered from selenium toxicity.
Because it is so rare, and commonly misdiagnosed,  exactly how many people are affected by this disease is not known. The literature frequently cites that fewer than 200 cases have been reported, though a consensus is building that many more cases occur around the world than have been reported. History
The first known report of the condition came in 1838 in an article titled "A Boneless Arm" in what was then The Boston Medical and Surgical Journal (now The New England Journal of Medicine). It is a brief report chronicling the case of Mr. Brown who had, in 1819 at age 18 years, broken his right upper arm in an accident. The person had two subsequent accidents, which fractured the arm twice more "before the curative process had been completed." At the time of the report in 1838, the person was reported as having remarkable use of the arm, in spite of the humerus bone having apparently disappeared – X-rays did not yet exist. Thirty-four years later,  a follow-up report was published in the same journal, following Mr. Browns death from pneumonia at the age of 70 years. The person had requested the arm "be dissected and preserved for the benefit of medical science" and this report contains a detailed pathological description of the arm and shoulder. Abnormalities of the remaining bones of the arm and shoulder are noted and the authors report that the arteries, veins, and nerves appeared normal. No mention was made of lymphatic vessels.