What labs are checked when a patient presents with a seizure?

Laboratory Tests for Patients Presenting with Seizures

For patients presenting with seizures, laboratory testing should include serum glucose and sodium levels for all patients, as well as a pregnancy test for women of childbearing age. 1

Core Laboratory Tests

Essential Tests for All Patients

• Blood glucose: Most common metabolic abnormality in seizure patients 2, 1
• Serum sodium: Hyponatremia is a frequent abnormality identified in seizure patients 2, 1
• Pregnancy test: For all women of childbearing age 1

Additional Tests Based on Clinical Presentation

• Complete blood count: To evaluate for infection or bleeding disorders
• Basic metabolic panel: To assess renal function and other electrolytes
• Calcium and magnesium levels: If clinically indicated by history or exam findings 1
• Antiepileptic drug levels: For patients on seizure medications 1
• Toxicology screen: If substance use is suspected 1
• Creatine kinase (CK): To evaluate for rhabdomyolysis, especially after generalized tonic-clonic seizures 3, 4
• Troponin: Consider in older patients, as troponin elevations are common after seizures 4

Special Considerations

Patients with First-Time Seizures

The history and physical examination will predict the majority of patients who will have laboratory abnormalities 2. For otherwise healthy adult patients who have returned to baseline after a first-time seizure:

• Glucose abnormalities and hyponatremia are the most frequent abnormalities identified 2
• Laboratory testing is generally of low yield but still recommended as standard of care 2, 1

Patients with Known Seizure Disorders

• Antiepileptic drug levels: Essential to check in patients on medication for seizure disorders 1
• Serum glucose and electrolytes: To identify potential seizure triggers 1

High-Risk Populations

• Lumbar puncture: Recommended for patients who are immunocompromised or febrile to rule out CNS infection 1
• Expanded metabolic testing: For patients with altered mental status, fever, or new focal neurologic deficits 2

Diagnostic Algorithm

1. Initial assessment:

   • Airway, breathing, circulation
   • Vital signs including temperature
   • Neurological examination

2. Basic laboratory tests for all patients:

   • Serum glucose
   • Serum sodium
   • Pregnancy test (women of childbearing age)

3. Additional tests based on clinical presentation:

   • Altered mental status → Complete metabolic panel, toxicology screen
   • Fever → CBC, blood cultures, lumbar puncture
   • On seizure medications → Antiepileptic drug levels
   • After generalized tonic-clonic seizure → CK, consider troponin (especially in older patients)
   • Suspected substance use → Toxicology screen

Pitfalls and Caveats

• Relying solely on laboratory tests without proper clinical assessment may lead to missed diagnoses
• Normal laboratory values do not exclude seizure diagnosis
• Elevated CK levels have high specificity but only moderate sensitivity for generalized tonic-clonic seizures 3
• Prolactin testing (within 10-20 minutes after event) may help differentiate epileptic seizures from psychogenic non-epileptic seizures but is not routinely performed in emergency settings 3, 5
• Laboratory abnormalities may be the cause rather than the result of seizures, so interpretation must be made in clinical context

Remember that while laboratory testing is important, it should be complemented by appropriate neuroimaging (CT or MRI) based on clinical presentation, especially for first-time seizures 2, 1.