What laboratory tests are recommended for a patient presenting with symptoms concerning for seizures?

Laboratory Testing for Neurology Consult to Rule Out Seizures

For patients presenting with symptoms concerning for seizures, obtain serum glucose and sodium levels as the minimum essential laboratory tests, with additional testing guided by specific clinical risk factors. 1, 2

Core Laboratory Tests (All Patients)

Serum glucose is mandatory for all seizure evaluations, as hypoglycemia is one of the most common treatable causes of seizures and is frequently not predicted by history or physical examination alone. 1, 3, 4

Serum sodium must be checked in all patients, as hyponatremia is the most frequent electrolyte abnormality associated with seizures and can both cause and result from seizure activity. 1, 3, 2

Pregnancy test is required for all women of childbearing age, as pregnancy fundamentally affects testing decisions, disposition, and antiepileptic drug selection. 1, 3, 4

Risk-Stratified Additional Testing

For Patients with Known Medical Conditions

Extended electrolyte panel including calcium, magnesium, and phosphate should be obtained in patients with:

• Renal insufficiency 1, 2
• Malnutrition 1, 2
• Diuretic use 1, 2
• Suspected alcohol-related seizures (particularly magnesium) 2, 4

The evidence shows that routine calcium, magnesium, and phosphate testing in otherwise healthy patients has extremely low yield—one prospective study found only 2 cases of hypocalcemia in 136 patients, both in patients with obvious risk factors (cancer and renal failure). 1

For Immunocompromised or Febrile Patients

Complete blood count should be obtained to evaluate for infection or hematologic abnormalities. 3, 2

Basic metabolic panel including BUN and creatinine is indicated to assess renal function and acid-base status. 3, 2

Lumbar puncture must be performed after head CT in immunocompromised patients, as they have substantially higher rates of CNS infections presenting as seizures. 1, 3, 4 This also applies to patients with fever or signs of meningeal irritation, though one pediatric study found no cases of occult bacterial meningitis presenting solely as a simple seizure in immunocompetent patients. 1

For Suspected Substance Use or Toxicity

Drug of abuse screen should be considered in first-time seizures when substance use is suspected, though prospective studies have not demonstrated benefit of routine screening. 1, 4 One retrospective review found that 69 of 90 patients with cocaine-related seizures had no prior seizure history. 1

Antiepileptic drug levels are indicated only in patients with known epilepsy to assess for medication non-compliance or subtherapeutic levels. 3

Toxicology screening is appropriate when medication overdose or withdrawal is suspected. 3, 2

Tests with Limited Utility in Routine Cases

Complete metabolic panels have remarkably low diagnostic yield in otherwise healthy patients who have returned to baseline neurologic status. 2, 4 One prospective study of 163 patients found only 1 unexpected case of hypoglycemia, with all other abnormalities predicted by history and physical examination. 2, 4

Creatine kinase has high specificity but only moderate sensitivity for generalized tonic-clonic seizures and is more useful for identifying complications like rhabdomyolysis than for diagnosis. 5

Prolactin testing can help differentiate epileptic seizures from psychogenic non-epileptic seizures in adults and adolescents with high specificity but moderate sensitivity, though this is typically not part of emergency evaluation. 5

Critical Pitfalls to Avoid

Do not assume alcohol withdrawal as the seizure etiology without excluding other causes, especially in first-time seizures—this should be a diagnosis of exclusion. 2, 4

Do not over-test patients who have returned to baseline neurologic status with normal examinations, as extensive laboratory panels rarely change management in this population. 1, 2, 4

Do not skip pregnancy testing in women of childbearing age, as one study identified 14 cases of gestational epilepsy (seizures occurring only during pregnancy) among 59 patients with new-onset seizures in pregnancy. 1

Neurophysiologic Testing

Emergent EEG should be considered specifically for:

• Suspected nonconvulsive status epilepticus 1, 3
• Subtle convulsive status epilepticus 1, 3
• Patients who received long-acting paralytics 1, 3
• Drug-induced coma 1, 3
• Persistent altered consciousness after seizure 3

Standard EEG is typically arranged through neurology consultation rather than performed emergently in the emergency department. 1