What labs should be ordered, besides CT imaging, for an ER patient presenting with new onset seizures and persistent headaches?

Laboratory Tests for ER Patient with New Onset Seizures and Persistent Headaches

For an ER patient presenting with new onset seizures and persistent headaches, essential laboratory tests should include serum glucose, electrolytes (especially sodium), complete blood count, calcium, renal function tests, and a toxicology screen. 1

Core Laboratory Workup

First-Line Laboratory Tests

• Blood Glucose: Hypoglycemia is a critical reversible cause of seizures that must be identified immediately 1, 2
• Serum Electrolytes: Particularly sodium levels, as hyponatremia is one of the most common metabolic abnormalities associated with seizures 1
• Complete Blood Count (CBC): To evaluate for infection or other systemic conditions 1
• Calcium: To rule out hypocalcemia as a potential seizure trigger 1
• Renal Function Tests: BUN and creatinine to assess kidney function 1, 3
• Liver Function Tests: To evaluate for metabolic causes and guide potential medication choices 3

Second-Line Laboratory Tests

• Toxicology Screen: Particularly important if history suggests possible substance use 1
• Creatine Kinase (CK): Has high specificity for generalized tonic-clonic seizures and helps monitor for rhabdomyolysis 3
• Magnesium: Consider in patients with malnutrition, alcoholism, or certain medications 1
• Pregnancy Test: For women of childbearing age, as pregnancy can affect seizure threshold and treatment decisions 1

Evidence-Based Approach

The American College of Emergency Physicians clinical policy emphasizes that laboratory testing should be guided by clinical findings 1. Studies have shown that glucose abnormalities and hyponatremia are the most frequent laboratory abnormalities identified in new-onset seizure patients, though most are predictable from history and physical examination 1.

Several prospective studies demonstrate the relatively low yield of routine laboratory testing in otherwise healthy patients with new-onset seizures who have returned to baseline mental status:

• In a study of 163 patients, only one unexpected case of hypoglycemia was discovered 1
• In another study of 136 patients, only two cases of unpredicted hypoglycemia were found 1
• A study of 247 patients identified only one case of unsuspected hypoglycemia 1

Special Considerations for Patients with Headaches

For patients with persistent headaches following seizures, additional considerations include:

• Lumbar Puncture: Should be considered if there are signs of meningeal irritation, fever, or if subarachnoid hemorrhage is suspected after normal CT imaging 1
• Inflammatory Markers: ESR/CRP if temporal arteritis or other inflammatory conditions are suspected

Clinical Pitfalls to Avoid

1. Don't rely solely on laboratory tests: History and physical examination remain crucial and will predict most laboratory abnormalities 1, 2

2. Don't miss treatable causes: Glucose abnormalities and electrolyte disturbances are the most common reversible metabolic causes of seizures 1

3. Don't overlook the significance of persistent headaches: Patients with focal neurological findings, persistent headache, and recent history of head trauma have a higher probability of structural abnormalities requiring imaging 1

4. Don't forget about potential drug interactions: If initiating antiepileptic medications, baseline laboratory values are important 3

5. Don't miss the opportunity to diagnose underlying conditions: Laboratory tests can identify symptomatic causes due to endocrine, metabolic, toxic, or infectious etiologies 3

The evidence clearly shows that while routine extensive laboratory testing has low yield in otherwise healthy patients who have returned to baseline, targeted testing based on clinical presentation is essential for identifying treatable causes and guiding management decisions.