To detect excessive exposure to mercury
When you have signs and symptoms of mercury poisoning or have been exposed to mercury; to monitor occupational exposure to mercury
A blood sample drawn from a vein in your arm and/or a random or 24-hour urine sample may be collected. Rarely, another sample such as hair, breast milk, or nails may be tested.
None needed; however, consult with your healthcare provider or laboratory about urine collection to avoid sample contamination.
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 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 the person's 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 eating 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 test used?
Mercury testing is used to detect the presence of an excessive amount of mercury in a person's blood and/or urine sample. It may be ordered by a healthcare practitioner to determine whether a person has had short-term exposure to a toxic level of mercury (acute exposure) or has been exposed over an extended period of time (chronic exposure). Testing may also be used to monitor those who may be exposed to mercury in the workplace.
To test for the various forms of mercury, more than one type of sample may be collected and tested.
- Blood is primarily tested to detect the presence of methyl mercury. Other forms of mercury (metallic and inorganic) can also be detected in the blood, but the amount present will decrease by half about every 3 days as the mercury moves into organs such as the brain and kidneys. Therefore, blood testing must be done within days of suspected exposure.
- Urine is used to test for metallic mercury and inorganic forms of mercury, but it cannot be used to determine exposure to methyl mercury.
- Hair testing may be useful to detect methyl mercury exposures that occurred several months previously, but hair testing is relatively complex and is not used frequently.
Although not routinely ordered tests, mercury has been shown to be present in nails, breast milk, stool, and breath.
Other general laboratory tests may be used to help evaluate the health of various organ systems in someone who has been exposed or thought to be exposed to toxic levels of mercury. Some examples include a comprehensive metabolic panel (CMP) and a complete blood count (CBC).
- When is it ordered?
Mercury testing may be ordered when a person has signs and symptoms suggesting excessive exposure to mercury. Acute signs and symptoms may include:
- Burning in the mouth and lungs
- Cough, difficulty breathing, chest tightness
- Difficulty urinating and decreased urine output
- Nausea, vomiting, diarrhea, or abdominal cramping
- Increased heart rate
- Fever or chills
Those who are chronically exposed may have nonspecific symptoms that involve the lungs, kidneys, and nervous system. Some of the chronic symptoms may include:
- Problems with hearing, taste and smell
- Blurry vision or sometimes tunnel vision
- Tingling or tremors in the arms or legs
- Difficulty walking
Testing may also be ordered even in the absence of symptoms when it is known that a person has been exposed to mercury in order to help evaluate the extent of the exposure.
Mercury measurements may be ordered on a regular basis to monitor people who work in industries that use mercury. It may be ordered, along with tests to detect lead and/or other heavy metals, for individuals who work with a variety of potentially hazardous materials.
- What does the test result mean?
Levels of mercury in blood and urine are normally very low. A test result showing no mercury or a low level indicates that it is likely that the person tested has not been exposed to excessive levels of mercury, at least not in the window of time that the test is measuring.
An increased blood level suggests a relatively recent exposure to mercury. In general, a blood level greater than 10 mcg/L indicates an unusual level of exposure for someone who does not regularly work with mercury.
In contrast to levels of mercury in the blood, a 24-hour urine sample gives more of an average past history of exposure to metallic or inorganic mercury. Normal urine levels are typically less than 10 mcg/L for someone without risk of occupational exposure. (For information on occupational exposure levels, see the Related Content section.)
Levels of mercury in either the blood or urine will not indicate the form or quantity of mercury to which a person was exposed.
An increased level of mercury in hair testing may indicate exposure to increased levels of methyl mercury, but hair samples are rarely used because of issues involving testing standardization, sample contamination, and the fact that hair is subject to many pre-analytical variables (hair exposure to dyes, bleach, shampoo, etc.).
- Is there anything else I should know?
Measures have been taken in recent years to reduce and control the public's exposure to mercury. Stricter regulations and recommendations have lowered the amounts allowable in the air, water, soil, food, and in the workplace.
- Is it ok for pregnant women and young children to eat fish?
The high levels of mercury found in certain fish may harm the developing nervous systems in unborn babies and young children. The U.S. Food and Drug Administration (FDA) recommends that pregnant women, women who may become pregnant, young children, and nursing mothers avoid eating fish with increased mercury levels, such as shark, swordfish, king mackerel and tilefish. It advises these groups to eat fish that are usually found to have lower levels of mercury such as canned light tuna, shrimp, or salmon. (See the Related Content section for their advice.)
- What is Thimerosal?
Thimerosal is an organic mercury compound that has been used in small amounts as a preservative in some vaccines. Although it is generally regarded as safe, the use of thimerosal is now being phased out. Thimerosal is no longer used as a preservative in any childhood vaccine, except for the influenza vaccine.
- Do silver teeth fillings contain mercury?
Yes. Dental amalgams (teeth fillings) are made up of about 50% metallic mercury. Some people feel that the tiny amount of mercury vapor released when a person chews may affect their health, but internationally most major health organizations feel that the amalgams are safe at this time. The U.S. Food and Drug Administration (FDA) has determined that dental amalgams are safe for adults and children over age 6. A few countries have begun to restrict their use as a precaution.
- What types of fish have higher levels of mercury?
Predator fish, those that eat other fish, have higher levels of mercury. Some of these include shark, swordfish, tilefish, and king mackerel. Some fish with lower levels of mercury include shrimp, canned light tuna, pollock, salmon, and catfish.
- What can I do to reduce my exposure to mercury?
In addition to avoiding consumption of fish known to harbor higher levels of mercury, you can avoid purchase and use of consumer products that contain mercury, such as thermostats and thermometers, and alternative medicines that contain mercury. These include some Hispanic folk remedies and Ayurvedic herbal preparations. Dispose of batteries, light-up novelty toys, thermometers, thermostats, and other mercury-containing items, including compact fluorescent light bulbs (CFLs), in hazardous waste facilities. Finally, exercise caution when handling CFLs, especially if you break one.