What is the recommended metabolic workup for a patient with seizures?

Recommended Metabolic Workup for Patients with Seizures

For adult patients presenting with seizures, the recommended metabolic workup should include serum glucose, sodium levels, and a pregnancy test for women of childbearing age, with additional testing guided by clinical presentation. 1

Core Laboratory Tests for All Seizure Patients

• Serum glucose and sodium: These are the most common metabolic abnormalities associated with seizures and should be routinely checked in all patients 1
• Pregnancy test: Required for all women of childbearing age as pregnancy can affect testing, disposition, and antiepileptic drug therapy 1

Additional Testing Based on Clinical Presentation

For Patients with Specific Risk Factors:

• Lumbar puncture: Recommended for immunocompromised patients (after head CT) and patients with fever or signs of meningeal irritation 1
• Drug of abuse screen: Consider in patients with first-time seizures, though evidence for routine use is limited 1
• Expanded electrolyte panel: Consider calcium, magnesium, and phosphate testing in patients with:
  • Known renal insufficiency 1
  • Malnutrition 1
  • Patients taking diuretics 1

Evidence and Rationale

The literature consistently shows that laboratory testing has a low yield in patients with new-onset seizures who have returned to baseline neurological status 1. Most abnormalities can be predicted by history and physical examination:

• Glucose abnormalities (hypoglycemia and hyperglycemia) are among the most frequent findings but are usually clinically apparent 1
• Hyponatremia is another common finding, typically predictable from clinical history 1
• Studies have found very few cases of unsuspected metabolic abnormalities:
  • One prospective study found only 1 unexpected case of hypoglycemia in 163 patients 1
  • Another study found 2 cases of unpredicted hypoglycemia in 136 patients 1

Special Considerations

Immunocompromised Patients

• Require more extensive evaluation including lumbar puncture 1
• HIV-positive patients have higher rates of CNS infections presenting with seizures 1

Alcohol-Related Seizures

• Alcohol withdrawal seizures should be a diagnosis of exclusion, especially in first-time seizures 1
• Consider checking magnesium levels in patients with suspected alcohol-related seizures 1

Common Pitfalls to Avoid

• Underestimating metabolic causes: While rare, treatable metabolic abnormalities can cause seizures and should be identified 2
• Over-testing: Routine extensive metabolic panels have low yield in otherwise healthy patients who have returned to baseline 1, 3
• Missing pregnancy: Failure to identify pregnancy can lead to inappropriate treatment decisions 1
• Neglecting lumbar puncture: In immunocompromised patients or those with fever, missing CNS infections can be fatal 1

Algorithm for Metabolic Workup in Seizure Patients

1. For all adult seizure patients:

   • Serum glucose and sodium 1
   • Pregnancy test for women of childbearing age 1

2. For patients with altered mental status, fever, or focal neurologic deficits:

   • Complete metabolic panel (including calcium, magnesium) 1, 2
   • Consider toxicology screen 1
   • Consider head CT and lumbar puncture as appropriate 1

3. For immunocompromised patients:

   • Complete metabolic panel 1
   • Head CT followed by lumbar puncture 1

4. For patients with known medical disorders (renal insufficiency, malnutrition) or taking diuretics:

   • Extended electrolyte panel including calcium, magnesium, phosphate 1

By following this evidence-based approach, clinicians can efficiently identify metabolic causes of seizures while avoiding unnecessary testing in patients who have returned to baseline neurological status.