Laboratory Testing for Seizure Patients
For all adult patients presenting with seizures, order serum glucose and sodium levels, and obtain a pregnancy test for women of childbearing age—these are the only universally recommended tests supported by guideline evidence. 1, 2, 3, 4
Core Laboratory Tests (All Patients)
- Serum glucose: This is the most common metabolic abnormality causing seizures and must be checked in all patients 1, 2, 3, 4
- Serum sodium: Hyponatremia is a frequent cause of seizures and should be tested universally 1, 2, 3, 4
- Pregnancy test: Required for all women of childbearing age, as this affects imaging decisions, disposition, and antiepileptic drug selection 1, 2, 3, 4
The American College of Emergency Physicians specifically recommends only these three tests for otherwise healthy adults with new-onset seizures who have returned to baseline neurologic status. 1
Risk-Stratified Additional Testing
Patients with Specific Risk Factors
Expand the metabolic panel (calcium, magnesium, phosphate, complete metabolic panel) if the patient has: 2, 3, 4
- Renal insufficiency
- Malnutrition
- Diuretic use
- Suspected alcohol-related seizures (magnesium is particularly important here)
Complete blood count: Order only if infection is suspected based on clinical presentation 2, 3
Drug/toxicology screen: Consider in first-time seizures with suspected substance use, though routine screening lacks strong evidence 1, 4
High-Risk Patients Requiring Extensive Workup
Immunocompromised patients require: 2, 3, 4
- Complete metabolic panel
- Head CT scan
- Lumbar puncture (after CT imaging)
Patients with fever or meningeal signs require: 2, 3, 4
- Lumbar puncture after head CT scan
- Complete blood count
Important Clinical Pitfalls
Laboratory testing has remarkably low yield in patients who have returned to baseline neurological status—most abnormalities are predictable from history and physical examination alone. 2, 4 One prospective study found only 1 unexpected case of hypoglycemia in 163 patients, and another found only 2 cases of unpredicted hypoglycemia in 136 patients. 4
Avoid routine "seizure panels": The evidence shows that calcium abnormalities are rare (only 2 cases of hypocalcemia found in 136 patients with new-onset seizures, both predictable from history—one with cancer, one with renal failure). 1 Extended electrolyte testing should be reserved for patients with specific risk factors, not ordered routinely.
Don't forget neuroimaging: While not a laboratory test, head CT is recommended for all older adults with new-onset seizures, and emergent CT is indicated for patients with postictal focal deficits that don't quickly resolve, history of malignancy, anticoagulant use, or immunocompromised status. 2, 3 MRI is preferred when available and when CT is negative but clinical suspicion remains high. 2, 3
Special Diagnostic Considerations
Prolactin and creatine kinase can help differentiate epileptic seizures from psychogenic non-epileptic seizures in the post-ictal period, with CK elevations being particularly common after generalized tonic-clonic seizures. 5 However, these are not part of the initial emergency evaluation and are more useful for diagnostic clarification after the acute event.
Lumbar puncture should NOT be performed routinely in alert, oriented, afebrile, immunocompetent patients—there is no evidence of occult bacterial meningitis presenting solely as a simple seizure. 1