Lead Poisoning

Diagnosis

Indications for Testing

• Known lead exposures per CDC recommendations for children
• Occupational exposures

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 exclude the potential contribution of external contamination
  • Concentrations ≥5 μg/dL are excessive for children and child-bearing females
  • The Biological Exposure Index (ACGIH guidelines, 2007) for whole blood lead levels in non-pregnant adults is 30 μg/dL
• Urine lead testing may be useful for detecting recent exposures to lead or monitoring chelation therapy

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

Differential Diagnosis

• Porphyria
• Other heavy metal toxicity (eg, arsenic)

Screening

Monitoring

Clinical Background

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 lower blood-lead concentrations in the U.S.

Epidemiology

• Prevalence – an estimated 450,000 children in the U.S. have concentrations ≥5 μg/dL (CDC, 2012)
• The Fourth National Report on Human Exposure to Environmental Chemicals (CDC, 2004) identified the 95th percentile for blood-lead concentration for various age groups
  • Children 1-5 years – 5.1 μg/dL
  • Children 6-11 years – 3.3 μg/dL
  • Children 12-19 years – 2.6 μg/dL
  • Adults 20 years and older – 4.3 μg/dL

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 ceramics with lead-based glaze
  • 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
    • Absorption is enhanced in children <6 years
    • Absorption may be lessened by adequate intake of iron, calcium, magnesium, alcohol, fat
• Absorbed lead remains bound to erythrocytes for approximately one month and then distributes into soft tissues such as liver, kidney, and brain over 4-6 weeks
• Final storage of absorbed lead
  • Bone
    • Children – 70% of absorbed lead
    • Adults – 80-95% of absorbed lead
  • Soft tissue sites
    • Store remaining absorbed lead 

Clinical Presentation

• Children – clinical symptoms usually present with concentrations ≥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 ≥10 μg/dL
    • Children who have been exposed to lead may have severe, persistent cognitive and behavioral problems
  • Hematologic – anemia
  • Renal – acute nephropathy
• Adults – whole blood concentrations ≥30 μg/dL indicate significant exposure (WHO)
  • Central nervous system – peripheral neuropathies, motor weakness
  • Renal – chronic renal insufficiency
  • Cardiovascular – systolic hypertension
  • Hematologic – anemia (normochromic/normocytic)
  • Gastrointestinal – abdominal pain, constipation, anorexia, nausea
• Blood lead in children and adults

  Blood Lead in Children and Adults*
  Lead Total	Comment
  5.0-9.9 μg/dL	Adverse health effects are possible, particularly in children <6 years and pregnant women. Discuss health risks associated with continued lead exposure. For children and women who are or may become pregnant, reduce lead exposure.
  10.0-19.9 μg/dL	Reduced lead exposure and increased biological monitoring are recommended.
  20.0-69.9 μg/dL	Removal from lead exposure and prompt medical evaluation are recommended. Consider chelation therapy when concentrations >50 μg/dL and symptoms of lead toxicity are present.
  >69.9 μg/dL	Critical. Immediate medical evaluation is recommended. Consider chelation therapy when symptoms of lead toxicity are present.
  * Sources of reference interval and interpretive comments include the CDC Guidelines for Screening Children for Blood Lead (1997) and the Recommendations for Medical Management of Adult Lead Exposure, Environmental Health Perspectives (2007). Thresholds and time intervals for retesting, medical evaluation, and response vary by state and regulatory body. Contact your State Department of Health and/or applicable regulatory agency for specific guidance on medical management recommendations. Elevated results may be due to skin or collection-related contamination. Elevated levels of blood lead should be confirmed with a venous specimen collected in a lead-free tube.

Treatment

• Chelation has been mainstay of treatment
  • Indicated in patients with concentrations ≥45 μg/dL
  • Chelation in patients with concentrations <45 μg/dL has not been proven to alter neurotoxicity
• Remove source of lead exposure

Indications for Laboratory Testing

• Tests generally appear in the order most useful for common clinical situations
• Click on number for test-specific information in the ARUP Laboratory Test Directory

Click the plus sign to expand the table of additional tests.

Test Name and Number	Comments
Heavy Metals Panel 3, Blood 0099470 Method: Quantitative Atomic Absorption/Quantitative Inductively Coupled Plasma-Mass Spectrometry
Heavy Metals Panel 3, Urine with Reflex to Arsenic Fractionated 0099475 Method: Quantitative Inductively Coupled Plasma-Mass Spectrometry
Heavy Metals Panel 4, Blood 0020584 Method: Quantitative Atomic Absorption/Quantitative Inductively Coupled Plasma-Mass Spectrometry
Heavy Metals Panel 4, Urine with Reflex to Arsenic Fractionated 0020572 Method: Quantitative Inductively Coupled Plasma-Mass Spectrometry
Heavy Metals Panel 6, Urine with Reflex to Arsenic Fractionated 0025055 Method: Quantitative Inductively Coupled Plasma-Mass Spectrometry
Lead Analysis, Nails 2007348 Method: Quantitative Inductively Coupled Plasma/Mass Spectrometry
Lead Analysis, Hair 2007346 Method: Quantitative Inductively Coupled Plasma-Mass Spectrometry
Zinc Protoporphyrin (ZPP), Whole Blood 0020605 Method: Quantitative Hematofluorometry
Zinc Protoporphyrin (ZPP), Whole Blood Industrial 0020614 Method: Quantitative Hematofluorometry
Erythrocyte Porphyrin (EP), Whole Blood 0020610 Method: Fluorometry