Blood lead level

Blood lead level (BLL), is a measure of the amount of lead in the blood. Lead is a toxic heavy metal and can cause neurological damage, especially among children, at any detectable level. High lead levels cause decreased vitamin D and haemoglobin synthesis as well as anemia, acute central nervous system disorders, and possibly death. Pre-industrial human BLL measurements are estimated to have been 0.016 µg/dL, and this level increased markedly in the aftermath of the industrial revolution. At the end of the late 20th century, BLL 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 BLL measurements above 25 µg/dL. No level of lead in the blood of children is currently thought to be safe, but the US Centers for Disease Control and Prevention (CDC) identified 10 μg/dL as a level of concern before 2012, and since 2012 has identified 5 μg/dL as an amount of lead that should prompt further medical investigation. Approximately 1 in 40 American children have at least this much lead in their blood. Measuring a person's blood lead level requires a blood sample, which may be performed with a fingerstick or a blood draw. The amount of lead found in the blood sample may 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). BLL cannot measure long-term lead exposure. An x-ray fluorescence test provides measurements from the bone because lead is predominantly stored in the human body in calcified tissues such as bones. The Centers for Disease Control and Prevention (CDC) changed its view on blood lead levels in 2012 because of 'a growing body of studies concluding that blood lead levels (BLLs) lower than 10 μg/dL harm children' with 'irreversible' effects, and 'since no safe blood lead level in children has been identified, a blood lead 'level of concern' cannot be used to define individuals in need of intervention'. The new policy is to aim to reduce average blood lead levels in US children to as low a level as possible. The CDC now publishes a 'reference' blood lead level which they hope can decrease in coming years. The reference value is 'based on the 97.5th percentile of the BLL distribution among children 1–5 years old in the United States'. It is currently 5 μg/dL. According to the CDC, in 2012, 'approximately 450,000 children in the United States have BLLs higher than this reference value'. There were more than 24 million US children under the age of 6 in 2014. If 2.5% are assumed to have blood lead levels higher than the reference amount, then there were approximately 600,000 US children with elevated blood lead levels in 2014. It is not a level deemed by the CDC as 'safe'. The reference level is designed to be used as a policy tool. Parents, clinicians, communities, state and federal authorities and political leaders are expected to monitor blood lead test levels, aware that children testing higher than the reference level are testing higher than 97.5% of all US children. The CDC expects action to be taken when test levels are found to exceed the reference. As blood lead levels slowly decline in response to such action, the reference will also decline. CDC will recalculate a new reference every four years. Prior to the industrial revolution human BLL is estimated to have been far less than it is today. Bone lead measurements from two Native American populations living on the Pacific coast and the Colorado River between 1000 and 1300 A.D. show that BLLs would have been approximately 0.016 µg/dL. The World Health Organization and others interpret these measurements to be broadly representative of human preindustrial BLL.