What diagnostic labs are recommended for a comprehensive seizure workup?

Diagnostic Labs for Seizure Workup

For a comprehensive seizure workup, serum glucose and sodium levels should be obtained in all patients with new-onset seizures, along with a pregnancy test for women of childbearing age. 1

Essential Laboratory Tests for All Seizure Patients

• Serum glucose: Hypoglycemia is one of the most common treatable metabolic causes of seizures and should be checked immediately 2
• Serum sodium: Hyponatremia can both cause and result from seizure activity 1, 2
• Pregnancy test: Required for all women of childbearing age as pregnancy may affect testing, disposition, and antiepileptic drug therapy 1, 2

Additional Laboratory Tests Based on Clinical Presentation

For Patients with Suspected Metabolic Abnormalities:

• Complete metabolic panel: To evaluate for electrolyte disturbances, renal and liver function 2
• Calcium levels: Consider in patients with cancer or renal failure 1
• Magnesium levels: Consider in patients with alcohol-related seizures 1

For Patients with Suspected Substance Use:

• Toxicology screening: Consider in patients with suspected substance use, though routine use has not been proven beneficial 1, 2
• Antiepileptic drug levels: Check in patients with known epilepsy to assess for medication non-compliance 2

For Patients with Suspected Infection:

• Complete blood count: To evaluate for infection or hematologic abnormalities 2
• Lumbar puncture: Indicated for immunocompromised patients, those with fever, or suspected central nervous system infection 1, 2

Diagnostic Imaging Considerations

• Head CT scan: Consider in patients with new-onset seizures, especially those with focal neurologic deficits, history of trauma, or immunocompromised status 1
• MRI: Preferred imaging modality for detailed evaluation, especially for refractory seizures or when a structural abnormality is suspected 1

Special Considerations for Different Patient Populations

For Children:

• In neurologically normal children with generalized seizures, extensive laboratory testing is rarely indicated as the yield of positive findings is low 1
• For children with focal seizures or abnormal neurological examination, more comprehensive testing is warranted 1

For Patients with Status Epilepticus:

• More urgent and comprehensive laboratory evaluation is required, including arterial blood gas in patients with respiratory compromise 2
• Emergent EEG should be considered in patients with persistent altered consciousness or suspected nonconvulsive status epilepticus 2

Common Pitfalls to Avoid

• Relying solely on laboratory tests to diagnose seizures - clinical history remains paramount 3
• Failing to check glucose and sodium in all seizure patients - these are the most common treatable metabolic causes 1, 2
• Overlooking the need for pregnancy testing in women of childbearing age 1
• Performing extensive laboratory testing in patients with known epilepsy having typical seizures without clinical changes 4

Diagnostic Algorithm

1. Obtain serum glucose and sodium in all patients with new-onset seizures 1
2. Perform pregnancy test in all women of childbearing age 1
3. Consider additional testing based on clinical presentation:
   • For suspected metabolic causes: Complete metabolic panel, calcium, magnesium 1
   • For suspected substance use: Toxicology screen 1
   • For suspected infection: CBC, lumbar puncture if indicated 1, 2
4. Consider neuroimaging (CT or MRI) based on clinical presentation 1
5. Consider EEG for further characterization of seizure type 1, 2

Remember that laboratory abnormalities may be the result rather than the cause of seizures, particularly with prolonged or multiple seizures 4, 5.