Lead poisoning or lead toxicity generally occurs in two settings - childhood exposure or occupational exposure. The removal of lead from paint and gasoline in the 1970s resulted in the lowering of lead blood concentrations in the U.S.

Epidemiology

• Prevalence - estimated  >450,000 children have levels greater than or equal to 10 µg/dL (Centers for Disease Control)

Risk Factors

• Children - main source of exposure is leaded paint
  • Living in older housing, generally inner city areas
  • Low income family
  • Midwest/Northeast residence
• Adults - main source of exposure is occupational
  • Lead smelting, mining, ammunitions, soldering, plumbing, ceramic glazing, construction workers
  • Use of lead-glazed ceramics
  • Use of herbal remedies from Asia

Pathophysiology

• Exposure mainly through respiratory and gastrointestinal tracts
  • 30-40% of inhaled lead is absorbed
  • Gut absorption depends on nutritional status and age
    • Impaired absorption may occur from intake of iron, calcium, magnesium, alcohol, fat
    • Enhanced absorption in children under 6 years
• Circulating lead is bound to erythrocytes for 30-35 days then dispersed into soft tissue such as liver, renal, brain
• Final storage of absorbed lead
  • Bone
    • In adults, 80-95% of absorbed lead
    • In children, 70% of absorbed lead
  • Soft tissue sites
    • Remainder of absorbed lead 

Clinical Presentation

• Children - clinical symptoms usually present with concentrations greater than or equal to 60 µg/dL but may occur at much lower concentrations
  • Gastrointestinal - abdominal pain, constipation, colic
  • Central nervous system - clumsiness, gait abnormalities, headache, behavioral changes, seizures
    • IQ declines seen at concentrations greater than or equal to 10 µg/dL
    • Children who have been exposed to lead may have severe, persistent cognitive and behavioral problems
  • Hematologic - anemia
  • Renal - acute nephropathy
• Adults
  • Central nervous system - peripheral neuropathies, motor weakness
  • Renal - chronic renal insufficiency
  • Cardiovascular - systolic hypertension
  • Hematologic - anemia
  • Gastrointestinal - abdominal pain, constipation, anorexia, nausea

Treatment

• Chelation has been mainstay of treatment
  • Indicated in patients with concentrationsgreater than or equal to 45 µg/dL because chelation in lower concentrations has never been proven to alter neurotoxicity
• Remove source of lead exposure

Diagnosis

• Indications for testing - known lead exposures, as per CDC recommendations for children
• Laboratory testing
  • Whole blood lead is the specimen of choice
    • Elevated lead concentrations in capillary blood specimens should be confirmed with a venous specimen to avoid the potential contribution of external contamination
    • Current CDC guidelines consider concentrations greater than or equal to 10 µg/dL excessive for children and child-bearing females
    • The Biological Exposure Index (ACGIH Guidelines, 2007) for whole blood lead in non-pregnant adults is 30 µg/dL
  • Urine lead may be useful for detecting recent exposures to lead or to monitor chelation therapy
  • Other testing such as plasma aminolevulinic acid, whole blood zinc protoporphyrin (ZPP) or free erythrocyte protoporphyrins may be useful for screening in occupational exposures
    • Presence not detected until lead concentrations reach greater than or equal to 35 µg/dL
  • Non-invasive measurements of lead in bone may be available via X-ray fluorescence
• Imaging studies
  • Non-invasive measurements of lead in bone may be available via K-shell X-ray fluorescence - not widely available except in research settings
• Disease screening
  • American Academy of Pediatrics recommends screening for all Medicaid children between 1-2 years of age; however, U.S. preventive services task force found insufficient evidence for or against screening
  • CDC criteria for non-Medicaid children is based on specific localities

Differential Diagnosis

• Porphyria
• Other heavy metal toxicity