What laboratory tests should be ordered for a patient presenting with seizures?

Laboratory Tests for Patients Presenting with Seizures

For patients presenting with seizures, essential laboratory tests should include serum glucose, serum sodium, complete metabolic panel, pregnancy test (for women of childbearing age), toxicology screen, CBC, blood cultures (if fever present), antiepileptic drug levels (if on medications), CK levels (after generalized tonic-clonic seizures), and troponin levels (in older patients). 1

Core Laboratory Evaluation

Essential Tests for All Patients

• Serum glucose: To rule out hypoglycemia as a cause of seizures 1
• Serum sodium: To identify hyponatremia or hypernatremia 1
• Complete metabolic panel: For patients with altered mental status to evaluate electrolytes, renal and liver function 1

Tests Based on Patient Characteristics

• Pregnancy test: For all women of childbearing age 1
• Toxicology screen: For patients with altered mental status or suspected substance use 1
• Antiepileptic drug levels: For patients already on seizure medications 1

Tests Based on Clinical Presentation

• CBC, blood cultures, lumbar puncture: For patients with fever to rule out infectious causes 1
• CK levels: After generalized tonic-clonic seizures to assess for rhabdomyolysis 1, 2
• Troponin levels: For older patients with generalized tonic-clonic seizures to assess for cardiac injury 1
• Prolactin levels: Can help differentiate epileptic seizures from psychogenic non-epileptic seizures if measured 10-20 minutes post-event 3, 2

Advanced Diagnostic Testing

Neuroimaging

• Non-contrast head CT: Urgent imaging for patients with suspected increased intracranial pressure or structural lesions 1
• MRI: Preferred imaging modality for non-emergent evaluation of new-onset seizures 1, 4

Neurophysiological Testing

• EEG: Should be performed within 24 hours after a seizure, with sleep EEG if waking EEG is normal 1, 3

Special Considerations

Lumbar Puncture

• Should be considered after ruling out increased intracranial pressure on imaging 1
• Indicated when meningitis or encephalitis is suspected 1
• CSF analysis should include cell count, protein, glucose, culture, and viral PCR panel 1

Metabolic Testing

• Ammonia and lactate may have diagnostic potential as postictal blood tests 2
• Magnesium levels should be checked, particularly in alcohol-related seizures 5

Clinical Pearls and Pitfalls

• Pitfall: Routine laboratory testing in children with seizures rarely identifies the cause and may not change management 6
• Pearl: Most abnormal laboratory values in seizure patients can be predicted by history and physical examination 5
• Caution: Non-convulsive status epilepticus should be considered in any patient with unexplained confusion or coma, requiring prompt EEG 7
• Important: Seizures may be the presenting symptom of various medical conditions including organ failure, electrolyte imbalance, medication effects, or toxic exposures 7

Algorithmic Approach

1. First-line tests (all patients): Serum glucose, sodium, complete metabolic panel
2. Second-line tests (based on clinical presentation):
   • If fever present: CBC, blood cultures, consider lumbar puncture
   • If altered mental status: Toxicology screen
   • If on seizure medications: Antiepileptic drug levels
   • If generalized tonic-clonic seizure: CK levels, troponin (in older patients)
3. Neuroimaging:
   • Urgent CT if increased intracranial pressure suspected
   • MRI for comprehensive evaluation of new-onset seizures
4. Neurophysiological testing:
   • EEG within 24 hours of seizure

This approach ensures comprehensive evaluation while avoiding unnecessary testing, focusing on identifying treatable causes and guiding appropriate management decisions.