What laboratory tests should be ordered for a patient with new onset seizure?

Laboratory Tests for New Onset Seizure

For all adult patients with new onset seizure, serum glucose and sodium tests should be ordered as the core laboratory workup, along with a pregnancy test for women of childbearing age. 1

Core Laboratory Tests

• Serum glucose and sodium are the most common metabolic abnormalities associated with seizures and should be checked in all patients 1
• Pregnancy test for all women of childbearing age, as pregnancy affects testing, disposition, and potential antiepileptic drug therapy 1
• Despite routine practice in many institutions, studies show that laboratory testing has a low yield in patients who have returned to baseline neurological status 1, 2

Additional Testing Based on Clinical Presentation

• For patients with suspected alcohol-related seizures:

  • Check magnesium levels, as hypomagnesemia is common in this population 3, 1
  • Remember that alcohol withdrawal seizures should be a diagnosis of exclusion, especially in first-time seizures 1

• For immunocompromised patients:

  • Complete metabolic panel 1
  • Head CT followed by lumbar puncture due to higher rates of CNS infections presenting with seizures 1, 4

• For patients with fever or signs of meningeal irritation:

  • Lumbar puncture after head CT to rule out infectious causes 1, 4

• For patients with altered mental status or focal neurologic deficits:

  • Complete metabolic panel 1
  • Toxicology screen 1, 4
  • Head CT 4

Neuroimaging Considerations

• MRI is the preferred imaging modality for new onset seizures if available 3
• Emergent neuroimaging should be performed in patients with postictal focal deficits that do not quickly resolve 3
• CT scan should be considered when acute intracranial bleeding is suspected 5

Special Considerations

• Expanded electrolyte panel (including calcium, magnesium, and phosphate) should be considered in patients with:

  • Known renal insufficiency 1
  • Malnutrition 1
  • Those taking diuretics 1

• Drug of abuse screen should be considered in patients with first-time seizures, though evidence for routine use is limited 1

Common Pitfalls and Caveats

• Most metabolic abnormalities causing seizures are predictable from history and physical examination 1, 2
• In one prospective study, only 1 unexpected case of hypoglycemia was found in 163 patients 2
• Routine serum chemistries in patients presenting to the ED with seizures who have returned to baseline are of extremely low yield 2
• Avoid over-testing patients with a normal neurologic examination and no risk factors 5
• Remember that over 50% of first seizures have an acute symptomatic cause, including metabolic, toxic, or infectious etiologies 6

Algorithm for Laboratory Workup

1. For all patients with new onset seizure:

   • Serum glucose and sodium 1
   • Pregnancy test for women of childbearing age 1

2. Add based on specific risk factors:

   • History of alcohol use: Add magnesium 1
   • Immunocompromised status: Complete metabolic panel, head CT, lumbar puncture 1
   • Fever/meningeal signs: Head CT followed by lumbar puncture 1, 4
   • Altered mental status: Complete metabolic panel, toxicology screen 1
   • Taking diuretics or known electrolyte disorders: Extended electrolyte panel (calcium, magnesium, phosphate) 1
   • Suspected drug use: Toxicology screen 1, 4