What lab findings and treatment are expected in a patient with a seizure episode, considering underlying conditions such as epilepsy, head trauma, hyponatremia, hypoglycemia, or hypocalcemia?

Laboratory Findings in Seizure Episodes

For all adult patients presenting with seizures, obtain serum glucose and sodium levels immediately, as these are the only laboratory tests that consistently alter acute management and have the highest yield for detecting treatable metabolic causes. 1, 2, 3

Essential Laboratory Tests for All Seizure Patients

• Serum glucose is mandatory for all patients, as hypoglycemia is one of the most common metabolic causes of seizures and requires immediate intervention 4, 1, 2

  • Prospective studies found unexpected hypoglycemia in 1-2 patients per 136-247 patients evaluated, though most cases are clinically predictable 4

• Serum sodium is mandatory for all patients, as hyponatremia can both cause and result from seizure activity 1, 2, 3

  • Hyponatremia is typically predictable from clinical history, with only 1 unexpected case found in 98 prospectively studied patients 4

• Pregnancy test is required for all women of childbearing age, as pregnancy affects testing decisions, disposition, and antiepileptic drug therapy 1, 2, 3

  • In one study, 14 of 59 patients with new-onset seizures in pregnancy had gestational epilepsy 4

Additional Laboratory Tests Based on Clinical Context

For Patients with Specific Risk Factors:

• Calcium levels should be obtained in patients with known cancer or renal failure 1, 2

  • Two cases of hypocalcemia were found in 136 patients with new-onset seizures (one with cancer, one with renal failure) 4

• Magnesium levels should be checked in patients with suspected alcohol-related seizures, as hypomagnesemia is common in this population 1, 2

• Complete metabolic panel (including calcium, magnesium, phosphate) should be considered in patients with renal insufficiency, malnutrition, or those taking diuretics 1, 2

• Toxicology screening should be considered in patients with first-time seizures when substance use is suspected, though routine use lacks proven benefit 4, 1, 2

  • In one retrospective review, 69 of 90 admitted patients with cocaine-related seizures had no prior seizure history 4

For High-Risk Patients:

• Lumbar puncture (after head CT) is recommended for immunocompromised patients to rule out CNS infection 1, 2, 3
  • Also indicated for patients with fever, meningeal signs, or persistent altered mental status 1, 2

Laboratory Findings with Low Yield

Routine comprehensive metabolic panels, CBC, and extended electrolyte testing have extremely low yield in otherwise healthy patients who have returned to baseline neurologic status. 4, 5

• In a prospective study of 163 patients, only 2 of 104 significant abnormalities (hypoglycemia and subdural hematoma) were not predicted by clinical examination 5

• History and physical examination predict the majority of patients who will have laboratory abnormalities 4

• There are no prospective studies supporting routine measurement of serum calcium, magnesium, or phosphate in otherwise healthy patients evaluated in the emergency department 4

Common Pitfalls to Avoid

• Do not miss hypoglycemia or hyponatremia - these are the only metabolic abnormalities that consistently require immediate intervention 3

• Alcohol withdrawal seizures should be a diagnosis of exclusion - especially in first-time seizures, always search for symptomatic causes before attributing to withdrawal 1, 3

• Do not obtain extensive laboratory testing in well-appearing patients - approximately 28-48% of suspected first seizures have alternative diagnoses (syncope, nonepileptic seizures, panic attacks), making careful history more valuable than laboratory tests 3

Treatment Considerations

• Benzodiazepines are first-line therapy for status epilepticus, followed by phenytoin/fosphenytoin, valproate, or levetiracetam 3

• Valproate (30 mg/kg) is as effective as phenytoin with potentially fewer adverse effects like hypotension 3

• Antiepileptic drug treatment reduces 1-2 year recurrence risk but does not affect long-term recurrence rates or remission rates, and starting treatment for a single seizure exposes patients to medication adverse effects without proven mortality or morbidity benefit 3

Seizure Recurrence Risk

• The mean time to first seizure recurrence is 121 minutes (median 90 minutes), with more than 85% of early recurrences occurring within 6 hours of ED presentation 3

• The overall 24-hour recurrence rate is 19%, decreasing to 9% when alcohol-related events and focal CT lesions are excluded 3

• Nonalcoholic patients with new-onset seizures have the lowest recurrence rate (9.4%), while alcoholic patients with seizure history have the highest (25.2%) 3