What are the diagnostic tests for mercury poisoning?

Diagnostic Tests for Mercury Poisoning

Blood and urine mercury levels are the primary diagnostic tests for confirming mercury poisoning, with additional testing determined by the exposure route and presenting symptoms.

Initial Assessment

History Taking

• Identify potential exposure sources:
  • Consumption of predatory fish (shark, swordfish, tilefish) 1
  • Occupational exposure (dental professionals, mining)
  • Environmental exposure (broken thermometers, spills)
  • Heating of mercury (stoves, ovens, furnaces) 2
  • Dental amalgams
  • Inappropriate handling of liquid mercury 3

Physical Examination

• Look for characteristic signs based on mercury form and exposure duration:
  • Acute symptoms: cough, dyspnea, chest pain, flu-like illness 2, 3
  • Chronic symptoms: tremor, rash, weight loss, cerebellar effects (ataxia, dysmetria) 1, 4
  • Severe cases: encephalopathy, nephrotic syndrome, polyneuropathy 3

Laboratory Testing

First-Line Tests

1. Blood mercury level

   • Normal range: 0-10 μg/dL 5
   • Limitations: May not reliably predict severity of toxicity, especially with chronic exposure 3
   • Most useful for recent or ongoing exposure

2. 24-hour urine mercury level

   • Better indicator for inorganic and elemental mercury exposure
   • More reliable for chronic exposure assessment

Additional Laboratory Tests

• Complete blood count
• Comprehensive metabolic panel
• Renal function tests (BUN, creatinine)
• Liver function tests
• Urinalysis (to assess for proteinuria)

Imaging Studies

• MRI of brain - preferred for evaluating cerebellar and cortical lesions in suspected mercury toxicity 1
• Chest X-ray - for patients with respiratory symptoms after vapor inhalation

Special Considerations

Testing Based on Mercury Form

1. Elemental mercury (vapor)

   • Primary tests: Blood and urine mercury levels
   • Environmental assessment for mercury contamination if exposure occurred in enclosed spaces 2

2. Inorganic mercury (salts)

   • Primary tests: Blood and urine mercury levels
   • Additional focus on renal function tests

3. Organic mercury (methylmercury)

   • Blood and hair mercury levels (hair provides historical exposure data)
   • Neurological assessment

Pregnant Women and Children

• Lower thresholds for testing should be applied
• More aggressive diagnostic approach due to increased vulnerability 1

Pitfalls and Caveats

1. Blood levels may be misleading

   • Blood mercury levels don't always correlate with clinical severity 3
   • Levels may normalize despite ongoing tissue toxicity

2. Delayed presentation

   • Symptoms may appear days to weeks after exposure, particularly with vapor inhalation 3

3. Environmental assessment

   • For suspected home/workplace exposure, environmental testing should be performed by health department or professional company 2

4. Misdiagnosis risk

   • Symptoms often mimic other conditions (flu, psychiatric disorders, neurological diseases)
   • Always consider mercury toxicity with unexplained neurological, renal, or multi-system symptoms

When to Refer

• Symptomatic patients should be referred to emergency department immediately 2
• Asymptomatic patients with high-dose or chronic exposure should be evaluated as outpatients 2
• Pregnant patients, even if asymptomatic, should be evaluated by their obstetrician 2

Mercury poisoning remains a diagnostic challenge that requires a high index of suspicion and appropriate testing strategy based on exposure history and clinical presentation.