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Lead

Lead poisoning is an environmental public health problem. Lead based paint was banned in 1978 and lead-based gasoline was phased out in 1986. Today, the most common source of lead poisoning is dust and paint chips created by deteriorating lead paint found in millions of homes built before 1978. Home renovation and demolition can also create airborne lead dust. Other sources of lead include soil contaminated by lead paint, some insecticides, and highway pollution. The water supply can become contaminated from lead pipes, fixtures, or solder. Food stored in poorly glazed pottery or grown in contaminated soil can be a major source of lead. Industrial sources of lead include the manufacture of lead acid batteries, secondary lead smelters, nonferrous foundries, and the refurbishing of lead painted structures. Lead is a potential hazard for ceramic artists. Employees of firing ranges are at risk due to the leaching of lead from bullets into the soil. Moonshine liquour may be contaminated with lead. Many Asian and Chinese herbal remedies are contaminated with heavy metals such as lead, arsenic, and mercury. Indian Aryurvedic medicines sold in the U.S. are also heavily contaminated with lead.

Lead enters the body primarily through ingestion and inhalation. Lead inhaled into the lungs is completely absorbed into the bloodstream. Young children are susceptible to lead ingestion because of frequent hand to mouth activities. Adults absorb 10 to 15% of ingested lead from the GI tract, while pregnant women and children absorb 50%. Iron or calcium deficiency and fasting greatly increase lead absorption. Lead is stored in the blood, soft tissues, and bone. Most lead is stored in bone as a labile component that readily exchanges with blood lead. Most of the blood lead is excreted in the urine. About 25% of blood lead is transferred to the soft tissues, where the average half life is 40 to 120 days. Bone lead has an average half-life of 15 to 20 years. Because of this long half-life, bone contains more than 95% of the body’s total lead burden. Following chronic lead exposure, blood lead levels may remain elevated for months or years after all sources of lead are removed from the environment because of the slow release of lead from the skeleton.

At low levels, lead poisoning in children may cause intelligence quotient deficiencies, reading and learning disabilities, impaired hearing, reduced attention span, hyperactivity, and behavior problems. Low level lead exposure from maternal blood may cause low birth weight and premature birth.

Acute lead toxicity may begin at blood lead levels of 40 to 60 ug/dL. Early symptoms include irritability, anorexia, malaise, and headache. As intoxication advances, abdominal pain and renal damage may develop. Peripheral neuropathy is characterized by extensor muscle weakness with minimal sensory loss. Intense exposure may cause cerebral edema, coma and death.

Universal screening for lead poisoning is recommended by the Centers for Disease Control for all children between the ages of 6 months and 6 years. Medicaid has mandated that its recipients be tested at ages 12 months and 24 months. Lead toxicity is defined as a blood lead level of10 ug/dL or greater in persons less than 18 years of age and a level of 25 ug/dL or greater in adults. Universal screening has been a public health success. The mean blood level in the U.S. between ages 1 and 74 has dropped from 1.28 ug/dL in 1976 to 2.8 ug/dL in 1991.

For children with elevated blood levels, blood tests are recommended every three months until a child has two consecutive levels below 10 ug/dL or three consecutive levels below 15 ug/dL.Environmental investigation is recommended for all children with blood lead levels of 20 ug/dL or higher or for children with two consecutive levels of 15 ug/dL tested three months apart. When the blood lead level rises to 50 ug/dL, OSHA requires mandatory removal from the exposure source. A person should not be allowed to come back to work until the level falls below 40 ug/dL or should be allowed to work in a lead free environment. Lead has a half life of 25 days in blood and complete removal from the source may lead to a 3 to 5 ug/dL reduction of blood lead level per week. Chelating therapy is rarely performed for blood lead concentrations below 60 ug/dL and is usually performed for levels of 80 ug/dL or higher.

Reference range is 0 to 10 ug/dL in children less than 16 years old and 0 to 20 ug/dL in adults. Blood levels higher than 20 ug/dL are considered toxic.

Specimen requirement is one royal blue top (EDTA) trace element blood collection tube or one metal free lavender top (EDTA) Microtainer. Fingerstick samples may give falsely elevated lead values if the skin is not thoroughly cleansed.

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