What labs should be ordered for a patient with seizures?

Essential Laboratory Tests for Seizure Patients

For patients with seizures, essential laboratory tests include serum glucose, serum sodium, complete metabolic panel, toxicology screen, CBC, pregnancy test in women of childbearing age, antiepileptic drug levels in patients on seizure medications, CK levels after generalized tonic-clonic seizures, and troponin levels in older patients with generalized seizures. 1

Core Laboratory Testing

The American College of Emergency Physicians and American Academy of Emergency Medicine recommend the following laboratory tests for seizure patients:

• Required for all patients:

  • Serum glucose (to rule out hypoglycemia)
  • Serum sodium (to identify hyponatremia)

• Required for specific populations:

  • Pregnancy test (all women of childbearing age)
  • Complete metabolic panel (patients with altered mental status)
  • Toxicology screen (patients with altered mental status or suspected substance use)
  • CBC and blood cultures (patients with fever)
  • Antiepileptic drug levels (patients on seizure medications)
  • CK levels (after generalized tonic-clonic seizures)
  • Troponin levels (older patients with generalized seizures) 1

Diagnostic Value of Laboratory Tests

Laboratory tests serve multiple important functions in seizure management:

1. Identifying acute symptomatic causes - Over 50% of first seizures have an acute symptomatic cause including metabolic, toxic, or infectious etiologies 2

2. Differentiating seizure types - Certain biomarkers help distinguish between epileptic and non-epileptic events:

   • Prolactin levels measured 10-20 minutes post-event have high specificity and moderate sensitivity for differentiating generalized tonic-clonic or partial seizures from psychogenic non-epileptic seizures 3, 4
   • Creatine kinase (CK) elevations are common after generalized tonic-clonic seizures with high specificity 3

3. Detecting complications - Laboratory analyses identify patients at risk for rare but serious complications such as rhabdomyolysis, acute renal failure, or cardiomyopathy 3

Additional Testing Considerations

• Lumbar puncture should be considered if infectious etiology is suspected, particularly with fever 1

• Toxicological screening is valuable when recreational drug or alcohol misuse is suspected, as failure to identify these triggers can lead to inappropriate antiepileptic drug treatment 2

• Metabolic markers such as ammonia and lactate may have diagnostic potential as postictal blood tests 3

Imaging and Other Diagnostic Tests

Beyond laboratory testing, the following are recommended:

• Brain imaging:

  • MRI is the preferred imaging study for new-onset seizures in non-emergent settings (American College of Radiology recommendation) 1
  • CT scan is indicated when severe structural lesion is suspected or etiology is unknown 4

• EEG should be performed within 24 hours after a seizure, with sleep EEG recommended if normal during wakefulness 4

Common Pitfalls to Avoid

1. Overreliance on laboratory tests - No postictal laboratory value can definitively prove or rule out the diagnosis of an epileptic seizure 3

2. Missing non-convulsive status - Non-convulsive status epilepticus should be considered in any patient with confusion or coma of unclear cause, requiring prompt EEG 5

3. Unnecessary testing - Laboratory tests and toxicological screening should be performed only when circumstances suggest metabolic or toxic encephalopathy 4

4. Neglecting medication-specific monitoring - For patients with established epilepsy on treatment, monitoring is needed for bone health and in situations where changes in AED clearance or metabolism are likely (extremes of age, pregnancy, comorbid disorders of renal or hepatic function) 2

By following this systematic approach to laboratory testing in seizure patients, clinicians can effectively identify underlying causes, guide appropriate treatment, and monitor for potential complications.