Index
It is a toxic heavy metal that can cause neurological damage, especially in children, at any detectable level.
The blood lead level is a measure of the amount of lead in the blood.
High lead levels cause decreased synthesis of vitamin D and hemoglobin, as well as anemia, acute central nervous system disorders, and possibly death.
Pre-industrial human blood lead level measurements are estimated to have been 0.016 μg / dL, and this level increased markedly after the industrial revolution. In the late 20th century, blood lead level measurements from remote human populations ranged from 0.8 to 3.2 μg / dL.
Children in populations adjacent to industrial centers in developing countries often have average blood lead level measurements above 25 μg / dL.
The blood lead level in children is currently not considered safe, but the Centers for Disease Control and Prevention identified 10 μg / dL as a level of concern before 2012, and as of 2012 identified 5 μg / dL as an amount of lead that should prompt further medical research.
About 1 in 40 American children have at least this amount of lead in their blood.
Measurement
Measuring a person’s blood lead level requires a blood sample, which can be done with a fingerstick or blood draw.
The amount of lead found in the blood sample can be measured in micrograms of lead per deciliter of blood (μg / dL) especially in the United States; 5 μg / dL is equivalent to 0.24 μmol / L (micromolar).
No safe level
The Centers for Disease Control and Prevention (CDC) changed its view on blood lead levels in 2012.
Due to a growing body of studies that conclude that blood lead levels below 10 µg / dL harm children with “irreversible” effects.
And since a safe blood lead level has not been identified in children, a blood lead “level of concern” cannot be used to define who needs intervention.
The new policy is to aim to reduce the average blood lead levels in American children to the lowest level possible.
The Centers for Disease Control and Prevention is now publishing a “baseline” blood lead level that they expect to decline in the coming years.
The reference value is “based on the 97.5th percentile of the distribution of blood lead level among children ages 1 to 5 in the United States.”
It is currently 5 μg / dL. According to the Centers for Disease Control and Prevention, in 2012, “approximately 450,000 children in the United States had blood lead levels higher than this guideline value.”
In 2014, there were more than 24 million American children under the age of 6. If 2.5% are assumed to have blood lead levels higher than the reference amount, then there were approximately 600,000 American children with elevated blood lead levels in 2014.
It is not a level considered “safe” by the Centers for Disease Control and Prevention. The reference level is designed to be used as a policy tool.
Parents, physicians, communities, state and federal authorities, and political leaders are expected to monitor blood lead levels, aware that children above the reference level get more than 97.5% of all American children.
The Centers for Disease Control and Prevention expects action to be taken when test levels exceed the reference.
As blood lead levels slowly drop in response to this action, the baseline will drop as well. The Centers for Disease Control and Prevention will recalculate a new benchmark every four years.
Historical trends
Before the industrial revolution, the level of lead in human blood was estimated to be much lower than it is today.
Lead measurements in the bones of two Native American populations living on the Pacific coast and the Colorado River between 1000-1300 am show that blood lead levels would have been approximately 0.016 μg / dL.
These measurements are interpreted by the World Health Organization and others to be broadly representative of the human pre-industrial blood lead level.
Contemporary levels of lead in human blood in remote locations are estimated at 0.8 and 3.2 μg / dL in the southern and northern hemispheres, respectively.
Blood lead levels 50 to 1,000 times higher than pre-industrial levels are commonly measured in contemporary human populations around the world.
The National Academies evaluated this issue in 1991 and confirmed that the blood lead level of the average person in the US was between 300 and 500 times that of pre-industrial humans.
Clair Patterson originally developed techniques for measuring small concentrations of lead in his quest to determine the age of the Earth. When he discovered that pre-industrial humans had much less lead in their bodies than all modern humans, he wrote:
‘It seems likely that people contaminated with amounts of lead that are at least 400 times higher than natural levels, and are almost a third of half of what is required to induce dysfunction, that their lives will be negatively affected by the loss of mental acuity and irrationality. ‘
This would apply to most people in the United States.
Demographic and geographic patterns
Blood lead levels are highest in countries where lead is added to gasoline, where lead is used in welded paint products, in urban areas, in areas adjacent to heavy traffic, and in developing countries.
In Jamaica, 44% of children living near lead production facilities had blood lead levels above 25 μg / dL.
In Albania, 98% of preschool-age children and 82% of schoolchildren had blood lead levels above 10 μg / dL; preschoolers living near a battery factory had average blood lead levels of 43 μg / dL.
In China, 50% of children living in rural areas had blood lead levels above 10 μg / dL, and children living near industrial and high-traffic sites had average blood lead levels of 22 to 68 μg / dL.
Blood lead level measurements in developed countries declined markedly in the late 1970s, when restrictions were placed on the use of lead in gasoline, gasoline, paint, solder, and other products.
In the United States, average blood lead levels measured among tens of thousands of subjects decreased from 12.8 to 2.8 μg / dL between 1976 and 1991. In the 1990s, the blood lead levels of children in Australia decreased. measured at 5 μg / dL, and 9 μg / dL in Barcelona, Spain.
In the United States, blood lead levels remain the highest for children, people in urban centers, people of lower socioeconomic status, and minorities.
Lead sources
Lead exposure occurs through ingestion, inhalation, and dermal contact. Lead enters the bloodstream through exposure and raises the level of lead in the blood which can cause lead poisoning or an elevated level of lead in the blood.
For example, a child can ingest lead by chewing on a toy that is made of lead-contaminated metal or painted with lead-contaminated paint.
A major source of lead exposure comes from inhalation. Factories and industries, vehicle exhaust (especially vehicles that use leaded gasoline), and even airborne dust that people breathe have the potential to contain lead.
Other important sources of lead exposure include ingestion and contact with products such as paint and soil that may contain lead. Many older claw foot bathtubs have also been found to leach lead, especially when filled with warm bath water.
Health effects
The Centers for Disease Control and Prevention states that a safe blood lead level in children has not been identified. Even low levels of lead in the blood have been shown to affect IQ, attention span, and academic performance. The effects of lead exposure cannot be corrected.
The absence of an identified blood lead level without harmful effects, combined with the evidence that these effects appear to be irreversible, underscores the critical importance of primary prevention. The most sensitive populations are infants, children, and pregnant women.
A child can drink a glass of water containing lead and absorb 50% of it. An adult can only retain 10% of the lead in that water. And once lead is in the child’s body, it reaches the brain through the not fully developed blood-brain barrier.
The body removes lead from the blood and stores it in the bone, but in children, it later leaves the bone more easily compared to adults.
The lead that accumulates in the bones of a woman is eliminated from her bones and passes freely from mother to child, the levels of maternal and fetal lead are practically identical. Once in the fetal circulation, lead readily enters the developing brain through the immature brain barrier.
Lead is associated with a wide range of toxicity in children across a wide range of exposures, down to the lowest blood lead concentrations studied, in both animals and people.
These toxic effects range from clinically obvious, symptomatic acute poisoning at high levels of exposure to subclinical (but still very damaging) effects at lower levels.
Lead poisoning can affect virtually every organ system in the body. The main organs affected are the central and peripheral nervous system and the cardiovascular, gastrointestinal, renal, endocrine, immune and hematological systems.
Adults who are exposed to dangerous amounts of lead can experience anemia, nervous system dysfunction, weakness, hypertension , kidney problems, decreased fertility , increased miscarriages, premature births, and low birth weight for their children.
A 2018 study in the American Economic Journal: Applied Economics found that for Rhode Island children born between 1997 and 2005 (and therefore exposed to historically low levels of lead).
“A one-unit decrease in average blood lead levels reduces the likelihood of being substantially below proficiency level in reading (math) by 0.96 (0.79) percentage points at a baseline of 12 (16) percent.” .
Lead poisoning
Lead poisoning is a type of metal poisoning caused by lead in the body. The brain is the most sensitive.
Symptoms can include abdominal pain, constipation , headaches, irritability, memory problems, inability to have children, and tingling in the hands and feet.
It causes almost 10% of intellectual disability of unknown cause and can lead to behavior problems. Some of the effects are permanent. In severe cases anemia, seizures, coma, or death can occur.
Lead exposure can occur from contaminated air, water, dust, food, or consumer products. Children are at higher risk, as they are more likely to put objects in their mouths, such as those containing lead paint, and absorb a greater proportion of the lead they consume.
Occupational exposure is a common cause of lead poisoning in adults in certain occupations with particular risk. Diagnosis is usually by measuring the level of lead in the blood.
The Centers for Disease Control (USA) have set the upper limit for blood lead for adults at 10 μg / dl (10 μg / 100 g) and for children at 5 μg / dl. Elevated lead can also be detected by changes in red blood cells or dense lines in children’s bones as seen on X-rays.
Treatment
This includes individual efforts such as removing lead-containing items from the home, workplace efforts such as better ventilation and monitoring, and national policies such as laws banning lead in products like paint and gasoline, reducing allowable levels in water or soil. , and provide for the cleaning of contaminated soil.
The main treatments are removing the source of lead and using drugs that bind to lead so that it can be removed from the body, known as chelation therapy.
Chelation therapy is recommended in children when blood levels are above 40-45 μg / dl. Medications used include dimercaprol, calcium disodium edetate, and succimer.
In 2013, lead is believed to have resulted in 853,000 deaths. It occurs most commonly in the developing world. Those who are poor are at greater risk. Lead is believed to account for 0.6% of the global burden of disease. People have been extracting and using lead for thousands of years.
Descriptions of lead poisoning date back to at least 2000 BC, while efforts to limit lead use date back to at least the 16th century. Concerns about low levels of exposure begin in the 1970s, as there is no safe threshold for lead exposure.
The amount of lead in the blood and tissues, as well as the length of time of exposure, determines toxicity. Lead poisoning can be acute (from short-term intense exposure) or chronic (from repeated low-level exposure over a long period of time), but the latter is much more common.
Diagnosis and treatment of lead exposure is based on the blood lead level (the amount of lead in the blood), measured in micrograms of lead per deciliter of blood (μg / dL).
Lead levels in urine can also be used, although less frequently. In cases of chronic exposure, the sequestrants often concentrate in the highest concentrations first in the bones, then in the kidneys.
If a provider performs a provocative excretion test, or “chelation test,” a measurement obtained from urine rather than blood is likely to provide a more accurate representation of the total lead load to a qualified interpreter.
The US Centers for Disease Control and Prevention and the World Health Organization state that a blood lead level of 10 μg / dL or higher is cause for concern.
However, lead can impair growth and have harmful health effects even at lower levels, and there is no known safe level of exposure. Authorities such as the American Academy of Pediatrics define lead poisoning as blood lead levels greater than 10 μg / dL.
Lead forms a variety of compounds and exists in the environment in various forms. The characteristics of intoxication vary depending on whether the agent is an organic compound (one that contains carbon) or an inorganic one.
Organic lead poisoning is now very rare, because countries around the world have phased out the use of organic lead compounds as gasoline additives, but such compounds are still used in industrial settings.
Organic lead compounds, which readily cross the skin and respiratory tract, predominantly affect the central nervous system.
Diagnosis
Diagnosis includes determining clinical signs and medical history, with investigation of possible routes of exposure. Clinical toxicologists, medical specialists in the area of poisoning, may be involved in diagnosis and treatment.
The main tool for diagnosing and evaluating the severity of lead poisoning is the laboratory analysis of the level of lead in the blood.
The blood test may reveal basophilic red blood cell stippling (dots on red blood cells visible through a microscope), as well as the changes normally associated with iron deficiency anemia (microcytosis and hypochromiasis).
However, basophilic stippling is also seen in unrelated conditions, such as megaloblastic anemia caused by vitamin B12 (colbalamin) and folate deficiencies.
Lead exposure can also be assessed by measuring erythrocyte protoporphyrin (EP) in blood samples. Erythrocyte protoporphyrin is a part of red blood cells that is known to increase when the amount of lead in the blood is high, with a delay of a few weeks.
Therefore, erythrocyte protoporphyrin levels together with blood lead levels may suggest the length of time of exposure; If blood lead levels are high, but erythrocyte protoporphyrin is still normal, this finding suggests that the exposure was recent.
However, the level of erythrocyte protoporphyrin alone is not sensitive enough to identify elevated blood lead levels below approximately 35 μg / dL.
Due to this higher threshold for detection and the fact that erythrocyte protoporphyrin levels also increase in iron deficiency, the use of this method to detect lead exposure has decreased.
Blood lead levels are an indicator primarily of recent or current lead exposure, not of total body burden. Lead in bone can be measured non-invasively using X-ray fluorescence. This may be the best measure of cumulative exposure and total body burden.
However, this method is not widely available and is used primarily for research rather than routine diagnosis.
Another radiographic sign of elevated lead levels is the presence of radiodense lines called lead lines in the metaphyses of the long bones of growing children, especially around the knees.
These lead lines, caused by increased calcification due to altered metabolism in growing bones, widen as the duration of lead exposure increases.
X-rays can also reveal foreign materials that contain lead, such as paint chips in the gastrointestinal tract.
Fecal lead content measured over the course of a few days can also be an accurate way to estimate the total amount of lead intake in childhood.
This form of measurement can serve as a useful way to see the level of oral lead exposure from all dietary and environmental sources of lead.
Lead poisoning shares symptoms with other conditions and can be easily missed.
Conditions that present similarly and must be ruled out to diagnose lead poisoning include carpal tunnel syndrome, Guillain-Barré syndrome, renal colic, appendicitis, encephalitis in adults, and viral gastroenteritis in children.
Other differential diagnoses in children include constipation, abdominal colic, iron deficiency, subdural hematoma, central nervous system neoplasms, emotional and behavioral disorders, and intellectual disability.
