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Also known as: Hg (chemical symbol)
Formal name: Mercury, Urine and Blood

The Test Sample

What is being tested?

Mercury is an element that can be toxic in various forms, which are tested in different samples:

  • Metallic or elemental mercury is a liquid often used in dental fillings, some thermometers, and batteries. Urine samples are typically tested to detect this form of mercury.
  • Inorganic mercury salts, which are produced by the reaction of non-carbon based compounds with mercury, are normally in a form of powder or crystal and sometimes used in topical preparations such as skin-lightening or antiseptic creams. Urine samples are usually used to detect this form of mercury.
  • Methyl mercury and other organic mercury compounds are products of reactions between mercury and carbon-based organic compounds. Bacteria with elevated levels of methyl mercury are often found in large, older, predator fish such as sharks and king mackerel. People who eat these fish may be exposed to this form of mercury. Blood is primarily used to identify a high level of methyl mercury.

Mercury is found in small quantities throughout the environment. It is released by the breakdown of minerals in rocks and soils and as a byproduct of fossil fuel combustion and waste incineration. It is inhaled with the air that we breathe, absorbed through the skin, and ingested with food. Mercury is also used in some mirror coatings, pharmaceuticals, and agricultural chemicals. Energy efficient compact fluorescent light (CFL) bulbs contain small amounts of mercury, which is also used to make electrical equipment, wire, and switching devices.

The tiny amounts to which the vast majority of people are exposed do not generally cause health concerns. However, people may develop mercury-related symptoms or complications if they are exposed to dangerous concentrations of mercury, such as might be found at a hazardous waste site, or are exposed chronically to mercury over long periods of time, especially if they work with heavy metals on the job.

Exposure to excessive amounts of mercury can be toxic. The amount of mercury absorbed by an individual and its effects on his or her health depends on the type of mercury, its concentration, and the nature of exposure. According to the Agency for Toxic Substances and Disease Registry (ATSDR), very little metallic mercury (less than 0.01%) is absorbed by the body, even if it is swallowed. However, if the same mercury is inhaled as a vapor, about 80% is absorbed into the bloodstream.

About 95% of methyl mercury, which is the type found in fish and other seafood, is absorbed by the digestive tract. The most common source of human exposure to methyl mercury is as consumption of contaminated seafood. Fish that come from contaminated waters and large predator fish that have eaten smaller fish may have significantly increased levels of methyl mercury. It is important to know the source of the fish that you consume and to limit the quantity of large predator fish eaten.

Once mercury is absorbed, the body may deposit it in a variety of body organs, including the kidneys and brain. The body will slowly rid itself of mercury through the urine and stool, but if an excessive amount accumulates, it can permanently damage the kidneys, nervous system, and brain.

Pregnant women with elevated levels of mercury can pass it on to their unborn baby, affecting development of the baby's brain, kidneys, and nerves especially. Mercury can also be passed from mother to baby through breast milk during nursing.

How is the sample collected for testing?

A blood sample is obtained by inserting a needle into a vein in the arm or a random or 24-hour urine sample may be collected. Rarely, another sample such as hair, breast milk, or nails may be tested.

NOTE: If undergoing medical tests makes you or someone you care for anxious, embarrassed, or even difficult to manage, you might consider reading one or more of the following articles: Coping with Test Pain, Discomfort, and Anxiety, Tips on Blood Testing, Tips to Help Children through Their Medical Tests, and Tips to Help the Elderly through Their Medical Tests.

Another article, Follow That Sample, provides a glimpse at the collection and processing of a blood sample and throat culture.

Is any test preparation needed to ensure the quality of the sample?

No test preparation is needed. Consult your healthcare provider or laboratory about urine collection to avoid sample contamination.