The diagnosis of lead intoxication is best confirmed by measuring lead in whole blood. Although this test reflects lead currently circulating in blood and soft tissues and is not a reliable marker of either recent or cumulative lead exposure, most patients with lead-related disease have blood lead concentrations higher than the normal range. Average background blood lead concentrations in North America and Europe have declined by 90% in recent decades, and the geometric mean blood lead concentration in the United States in 2011–2012 was estimated to be 0.973 mcg/dL. Though predominantly a research tool, the concentration of lead in bone assessed by noninvasive K X-ray fluorescence measurement of lead has been correlated with long-term cumulative lead exposure, and its relationship to numerous lead-related disorders is the subject of ongoing investigation. Measurement of lead excretion in the urine after a single dose of a chelating agent (sometimes called a “chelation challenge test”) primarily reflects the lead content of soft tissues and may not be a reliable marker of long-term lead exposure, remote past exposure, or skeletal lead burden. Accordingly, this test is rarely indicated in clinical practice. Because of the lag time associated with lead-induced elevations in circulating heme precursors, the finding of a blood lead concentration of 30 mcg/dL or more with no concurrent increase in zinc protoporphyrin suggests that the lead exposure was of recent onset.
B. Organolead Poisoning
Poisoning from organolead compounds is now very rare, in large part because of the worldwide phase-out of tetraethyl and tetra-methyl lead as antiknock additives in gasoline. However, organolead compounds such as lead stearate or lead naphthenate are still used in certain commercial processes. Because of their volatility or lipid solubility, organolead compounds tend to be well absorbed through either the respiratory tract or the skin. Organolead compounds predominantly target the CNS, producing dose-dependent effects that may include neurocognitive deficits, insomnia, delirium, hallucinations, tremor, convulsions, and death.
A. Inorganic Lead Poisoning
Treatment of inorganic lead poisoning involves immediate termination of exposure, supportive care, and the judicious use of chelation therapy. (Chelation is discussed later in this chapter.) Lead encephalopathy is a medical emergency that requires intensive supportive care. Cerebral edema may improve with corticosteroids and mannitol or hypertonic saline, and anticonvulsants may be required to treat seizures. Radiopacities on abdominal radiographs may suggest the presence of retained lead objects requiring gastrointestinal decontamination. Adequate urine flow should be maintained, but overhydration should be avoided. Intravenous edetate calcium disodium (CaNa2EDTA) is administered at a dosage of 1000–1500 mg/m2/d (approximately 30–50 mg/kg/d) by continuous infusion for up to 5 days. Some clinicians advocate
Production of lead began 6000 years ago, and lead poisoning is one of the oldest known occupational illnesses. Worldwide, lead production has doubled over the past two decades in part because of the growing demand for lead acid storage batteries. Efforts to prevent lead poisoning from multiple industrial, commercial, and environmental sources remain an active focus of public health in the USA.