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Mercury Poisoning (cont.)

Exams and Tests

Unfortunately, many people do not know they have been exposed to industrial or environmental sources of mercury. This makes the diagnosis difficult for the physician because many times the symptoms of mercury poisoning are subtle and may take weeks, months, or years to develop in some individuals. Consequently, physicians may order many different tests before, or at the same time as those listed below in an effort to diagnose the patient's condition from the many diseases [such as Parkinson's, amyotrophic lateral sclerosis (ALS, Lou Gehrig's Disease), dementia, and multiple sclerosis (MS)] and toxins (iron, arsenic, carbon monoxide) that produce one or more symptoms of mercury toxicity.

A through history and physical exam may alert the physician to the potential for mercury poisoning if tremors and erethism (several neuropsychiatric problems concurrently such as anxiety, depression, memory loss, excessive shyness, and irritability) are present. Acrodynia (rash, fever, irritability, splenomegaly, and muscle weakness) can be seen in patients, especially children, exposed to most forms of mercury poisoning. If the person knows or suspects mercury poisoning, the physician needs to be told immediately.

Acute mercury poisoning can be detected by measuring mercury levels in the blood; this test is usually done in a specialized laboratory. A normal mercury level is less than 10 µg/L (micrograms/liter) and less than 20µg/L in urine. Higher levels suggest toxic exposure. However, there are two problems with this test. First, the test on blood or urine should be performed five days or more after a person has stopped eating fish; because such a meal can raise the blood level of mercury higher than normal for a short (up to five days) time period. Second, it does not usually provide any valuable information about a previous short or chronic exposure. Further, urine tests are not reliable for measuring methylmercury or other compounds such as short-chained alkyl mercury compounds because they are mainly excreted in the feces and bile, respectively.

Tests to measure the ratio of mercury in blood plasma versus red blood cells is performed to help distinguish organic mercury poisoning from inorganic. Red cells concentrate organic mercury but not inorganic mercury compounds. The concentration of organic mercury in red cells is about 20 times that found in plasma; the concentration of inorganic mercury at maximum is only about twice that found in plasma.

Other tests that are usually ordered are a complete blood count (CBC) and a fecal blood detection test to help determine if anemia or gastrointestinal bleeding has occurred. Some doctors request an MRI scan to determine the extent of brain atrophy. X-rays are generally ordered for individuals that have ingested elemental mercury (for example, a broken mercury thermometer). X-rays show the movement and excretion of the X-ray opaque mercury.

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