Selenium

Ranges vary between laboratories (for example 0.8 to 2.0 or 0.9 to 1.65 umol/L), UK adults on an ordinary diet sit towards the lower half, and the value falls during any inflammation.

Selenium is a trace element built into a family of enzymes that protect cells from damage and help make active thyroid hormone. It comes from cereals, meat, fish, eggs and Brazil nuts, and UK soils are relatively low in it. Both shortage and excess are uncommon, and most testing is done in people who cannot absorb food normally or are fed intravenously.

It is requested in people on long-term intravenous or tube feeding, with poor absorption, after weight-loss surgery, on very restricted diets or on dialysis, when unexplained muscle or heart problems are being looked into, and on some private nutrition panels. Occasionally it is checked when too much selenium from supplements is a concern.

• Selenium supplements and eating a lot of Brazil nuts
• Some industrial exposures, rarely
• Higher meat and fish intake, slightly

• Any inflammation, infection or serious illness, which lowers it for days to weeks
• Long-term intravenous or tube feeding without added selenium
• Poor absorption, weight-loss surgery and chronic diarrhoea
• Very restricted or low-protein diets and eating disorders
• Dialysis and liver cirrhosis
• Pregnancy and heavy alcohol use, slightly

• A cold or any inflammation on the day of the test lowers it without touching the body's stores, so doctors often read it with CRP
• UK diets give values towards the lower end of ranges set elsewhere
• Blood collected in a standard tube rather than a trace-element tube can be contaminated

A sample in a trace-element tube, ideally not during an infection, often with CRP measured at the same time. Whole blood or red cell selenium is sometimes used to show longer-term status.

Written by a UK consultant physician. Typical UK adult reference ranges; your laboratory's own printed range takes precedence.