What labs should be ordered for a patient presenting with seizure activity?

Laboratory Tests for Patients Presenting with Seizure Activity

For patients presenting with seizure activity, the core laboratory tests should include serum glucose, sodium, pregnancy test for women of childbearing age, and additional tests based on clinical presentation and risk factors. 1, 2

Core Laboratory Tests for All Seizure Patients

• Serum glucose and sodium - these are the most common metabolic abnormalities associated with seizures and are recommended by the American College of Emergency Physicians for all adult patients with seizures 1, 3
• Pregnancy test for all women of childbearing age, as pregnancy can affect testing, disposition, and antiepileptic drug therapy 1, 3
• Complete blood count (CBC) to evaluate for infection or other hematologic abnormalities 2
• Basic metabolic panel, including BUN, creatinine, and electrolytes 2

Additional Testing Based on Clinical Presentation

• Calcium and magnesium levels should be checked, especially in patients with known renal insufficiency, malnutrition, those taking diuretics, or with suspected alcohol-related seizures 1, 2
• Drug of abuse screen should be considered in patients with first-time seizures, though evidence for routine use is limited 1, 3
• Extended electrolyte panel including phosphate for patients with renal insufficiency, malnutrition, or those taking diuretics 1, 2
• Lumbar puncture (after head CT) for patients who are:
  • Immunocompromised
  • Febrile
  • Showing signs of meningeal irritation 1, 3

Neuroimaging Considerations

• Head CT scan is recommended for patients with new-onset seizures, particularly older adults 2, 3
• MRI is preferred if available, particularly for patients with focal neurological deficits 2
• Emergent EEG should be considered in patients suspected of being in nonconvulsive status epilepticus or subtle convulsive status epilepticus 3

Special Considerations

• For suspected alcohol-related seizures, check magnesium levels as hypomagnesemia is common in this population 1, 2
• Alcohol withdrawal seizures should be a diagnosis of exclusion, especially in first-time seizures 2, 1
• Prolactin testing can help differentiate epileptic seizures from psychogenic non-epileptic seizures with high specificity and moderate sensitivity 4
• Creatine kinase (CK) levels are commonly elevated after generalized tonic-clonic seizures and have high specificity for seizure activity 4

Important Clinical Pitfalls

• Laboratory testing has a relatively low yield in patients who have returned to baseline neurological status, with most abnormalities predictable by history and physical examination 1, 2
• Studies have found very few cases of unsuspected metabolic abnormalities, with one prospective study finding only 1 unexpected case of hypoglycemia in 163 patients 1
• Metabolic epilepsies, though rare, should be considered in patients with very early onset epilepsy or predominantly myoclonic seizures 5
• Electrolyte imbalances may precede seizures - patients tend to be mildly hypocalcemic before seizures, and serum potassium typically increases during and after seizures 6
• Non-convulsive status epilepticus should be considered in any patient with confusion or coma of unclear cause 7

Algorithm for Laboratory Workup in Seizure Patients

1. For all seizure patients:

   • Serum glucose and sodium
   • Pregnancy test (women of childbearing age)
   • Complete blood count
   • Basic metabolic panel 1, 2

2. For patients with first-time seizures:

   • Add calcium, magnesium
   • Consider drug screen
   • Head CT scan 1, 2

3. For patients with specific risk factors:

   • Immunocompromised, febrile, or meningeal signs: Add lumbar puncture after head CT
   • Alcohol-related: Add magnesium level
   • Renal insufficiency/diuretics: Add extended electrolyte panel including phosphate
   • Altered mental status: Consider EEG 1, 2, 3