Arsenic (urine)

There is no level the body needs; UK labs print an upper limit of around 130 nmol/L (10 ug/L) for total urine arsenic in someone who has not eaten seafood, values of ten times that are common for a day or two after fish or shellfish, and some labs print the result per mmol of creatinine or separate out the harmless seafood form.

Arsenic is a metal-like element found naturally in some groundwater, soils, rice and, in a harmless organic form, in fish and shellfish. It leaves the body in the urine within a few days, so a urine test reflects recent exposure. The harmful inorganic form, from contaminated water, some old wood preservatives, pesticides and traditional remedies, affects the skin, nerves, blood and, over years, the risk of some cancers in the general population.

It is requested when exposure is possible, for example from a private water supply, certain jobs, traditional remedies or a suspected poisoning, and when unexplained skin changes, nerve problems, tummy upset or anaemia are being looked into. A blood arsenic is rarely useful because it clears so fast.

• Fish, shellfish and seaweed eaten in the previous two or three days, which raise the harmless organic form a great deal
• Drinking water from a contaminated private well or borehole
• Work with wood preservatives, pesticides, glass, metal smelting or semiconductors
• Some traditional Ayurvedic or Chinese remedies and some imported cosmetics
• A rice-heavy diet, slightly
• Old arsenic-treated timber, when sawn or burned

• Avoiding seafood for three days before the test
• Ending the exposure, after which the level falls within days
• A value below the cut-off is the expected finding

• A seafood meal in the previous few days is by far the commonest reason for a high result, which is why labs ask for seafood to be avoided beforehand and may split the result into organic and inorganic forms
• A concentrated or dilute urine moves the number, so some labs correct it to creatinine
• Rice-based diets raise it slightly

A spot or 24-hour urine sample after avoiding fish, shellfish and seaweed for at least three days. If the total is raised the lab can measure the different forms separately (speciation) to tell seafood arsenic from the harmful kind.

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