Lead Poisoning

Lead Poisoning

 

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 blood levels in the U.S.

Epidemiology

  • Incidence – estimated  >450,000 children have levels ≥10 μg/dL (Centers for Disease Control)

Risk factors

  • Children – main source of exposure is leaded paint
    • Low income family
    • Living in older housing, generally inner city areas
    • 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

Clinical presentation

  • Children – clinical symptoms usually present with levels ≥60 μg/dL but may occur at much lower levels
    • Gastrointestinal – abdominal pain, constipation, colic
    • Central nervous system – clumsiness, gait abnormalities, headache, behavioral changes, seizures
      • IQ declines seen at levels ≥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

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 

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

Diagnosis

  • Laboratory testing
    • Whole blood lead is the specimen of choice
      • Elevated lead levels in capillary blood specimens should be confirmed with a venous specimen to avoid the potential contribution of external contamination
      • Current CDC guidelines consider levels ≥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 levels reach ≥35 μg/dL
    • Non-invasive measurements of lead in bone may be available via X-ray fluorescence

Treatment

  • Chelation has been mainstay of treatment
    • Indicated in patients with levels ≥45 μg/dL because chelation in lower levels has never been proven to alter neurotoxicity
  • Remove source of lead exposure