What labs should I order for a patient having a seizure?

Laboratory Tests for Patients Having a Seizure

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

Core Laboratory Tests for All Seizure Patients

• Serum glucose: Critical to identify hypoglycemia, which can both cause seizures and occur as a complication 1, 2
• Serum sodium: Hyponatremia is a common cause of seizures 1, 3
• Complete metabolic panel: To assess electrolyte imbalances, renal and liver function 1, 3
• Pregnancy test: Required for all women of childbearing age 1

Additional Tests Based on Clinical Presentation

For patients with altered mental status:

• Toxicology screen: Essential to identify drug-induced seizures or withdrawal 1, 3
• Expanded metabolic workup: Including calcium, magnesium, phosphate 1

For patients with fever:

• Complete blood count (CBC): To identify infections 1
• Blood cultures: If systemic infection is suspected 1
• Lumbar puncture: Consider if CNS infection is suspected 1

For patients on seizure medications:

• Antiepileptic drug levels: To identify subtherapeutic levels or toxicity 1, 4

After generalized tonic-clonic seizures:

• Creatine kinase (CK): Elevated in 59.4% of patients after GTCS; helps identify rhabdomyolysis 1, 5, 6
• Troponin levels: Particularly important in older patients; elevated in 12% of tested patients 1, 6

Important Clinical Considerations

1. Timing of glucose testing: Evidence suggests that checking glucose before administering benzodiazepines for active seizures can cause significant treatment delays (median 2.1-5.9 minutes). While hypoglycemia must be ruled out, it is rare (1.2%) in seizure patients 2. Consider simultaneous glucose testing and benzodiazepine administration for actively seizing patients.

2. Interpretation of elevated markers:

   • CK elevations are common after GTCS (59.4% of patients) but significant rhabdomyolysis (>50-fold increase) occurs in only 1.9% 6
   • Troponin elevations occur in 12% of tested patients, with actual myocardial infarction being rare (<1%) 6

3. Pitfalls to avoid:

   • Don't delay treatment of active seizures to obtain laboratory tests
   • Don't assume all laboratory abnormalities are caused by the seizure; they may be the underlying cause
   • Don't forget to check antiepileptic drug levels in patients with known epilepsy
   • Be aware that non-convulsive status epilepticus should be considered in any patient with unexplained confusion or altered mental status 3

Follow-up Testing

For first-time seizures, additional diagnostic workup should include:

• Electroencephalography (EEG): Should be performed within 24-48 hours of the seizure 1
• Neuroimaging: MRI is preferred over CT for detecting brain abnormalities 1

By following this structured approach to laboratory testing in seizure patients, clinicians can effectively identify underlying causes and potential complications while ensuring timely treatment.