Laboratory Testing After a Seizure
For an otherwise healthy adult who has returned to baseline after a seizure, obtain serum glucose and sodium levels immediately, and perform a pregnancy test in women of childbearing age—these are the only laboratory tests consistently shown to alter acute management. 1, 2, 3
Essential Laboratory Tests (All Patients)
- Serum glucose must be checked immediately, as hypoglycemia is one of the most common treatable causes of seizures and requires immediate intervention 1, 4, 2
- Serum sodium should be evaluated in all seizure patients, as hyponatremia is a frequent abnormality that can both cause and result from seizure activity and consistently requires immediate intervention 1, 4, 2
- Pregnancy test is required for all women of childbearing age (post-menarche), as pregnancy affects testing decisions, disposition, and antiepileptic drug therapy 1, 2, 3
Additional Laboratory Tests (Based on Clinical Context)
The following tests should be obtained only when suggested by specific clinical findings, as they rarely alter acute management in otherwise healthy patients who have returned to baseline:
- Complete blood count should be performed if infection, anemia, or hematologic abnormalities are suspected based on history or examination 4
- Complete metabolic panel (including calcium, magnesium, phosphate) should be obtained in patients with:
- Toxicology screening should be considered if substance use, withdrawal, or medication overdose is suspected, though routine use has not been proven beneficial 1, 2, 5
- Antiepileptic drug levels should be checked in patients with known epilepsy to assess for medication non-compliance or subtherapeutic levels 4
Status Epilepticus or Persistent Altered Mental Status
For patients in status epilepticus or with persistent altered consciousness, more comprehensive testing is essential:
- Arterial blood gas should be performed if respiratory compromise or metabolic acidosis is suspected 4
- Basic metabolic panel to evaluate electrolyte disturbances, renal function, and acid-base status 4
- Creatine kinase (CK) levels are commonly elevated after generalized tonic-clonic seizures and display high specificity for differentiating epileptic seizures from psychogenic non-epileptic seizures 6
- Ammonia and lactate may have diagnostic potential for postictal blood tests 6
Lumbar Puncture Indications
- Perform lumbar puncture (after head CT) in immunocompromised patients to rule out CNS infection 1, 2, 3
- Consider lumbar puncture when there is concern for meningitis or encephalitis, particularly in febrile patients with meningeal signs 1, 2, 3
- Do not perform routine lumbar puncture in alert, oriented, afebrile, non-immunocompromised patients who have returned to baseline, as there are no cases of occult bacterial meningitis manifesting solely as a simple seizure 1
Critical Pitfalls to Avoid
- Do not order extensive routine laboratory testing (calcium, magnesium, phosphate, CBC, comprehensive metabolic panel) in otherwise healthy patients who have returned to baseline—prospective studies show these tests rarely alter management unless predicted by history and physical examination 1, 5
- Do not miss hypoglycemia or hyponatremia, as these are the only two laboratory abnormalities that consistently require immediate intervention 1, 3
- Do not assume alcohol withdrawal as the cause in first-time seizures without excluding other symptomatic causes first 3
- Consider alternative diagnoses, as 28-48% of suspected first seizures have alternative diagnoses such as syncope, psychogenic non-epileptic seizures, or panic attacks 3
Monitoring for Complications
For patients with generalized tonic-clonic seizures, consider measuring CK, electrolytes, creatinine, and liver/renal function tests on at least one occasion to identify those at risk for rare but threatening complications such as rhabdomyolysis, acute renal failure, or cardiomyopathy 6