What are the initial lab orders for an older adult presenting with new onset seizure?

Initial Laboratory Orders for Older Adults with New-Onset Seizures

For older adults presenting with new-onset seizures, the core laboratory tests should include serum glucose, sodium, and a complete metabolic panel, as these are the most common metabolic abnormalities associated with seizures. 1

Core Laboratory Tests

• Serum glucose and sodium tests are recommended for all adult patients with seizures, as these are the most common metabolic abnormalities associated with seizures 1
• Complete blood count (CBC) to evaluate for infection or other hematologic abnormalities 2
• Basic metabolic panel including BUN, creatinine, and electrolytes 2, 1
• Calcium and magnesium levels, especially important in older adults who may be taking medications that affect these electrolytes 2, 1
• Pregnancy test for women of childbearing age 1

Additional Testing Based on Clinical Presentation

• Drug screen should be considered in patients with first-time seizures, particularly if there is suspicion of substance use 1, 3
• Extended electrolyte panel including phosphate for patients with known renal insufficiency, malnutrition, or those taking diuretics 1
• Liver function tests to evaluate for hepatic causes of seizures 4
• Toxicology screening if medication toxicity is suspected 5

Neuroimaging

• Head CT scan should be performed in all older adults with new-onset seizures to evaluate for structural lesions 2, 1
• MRI is preferred if available, particularly for patients with focal neurological deficits or when CT is negative but clinical suspicion for structural abnormality remains high 1

Special Considerations for Older Adults

• Magnesium levels should be checked in patients with suspected alcohol-related seizures, as hypomagnesemia is common in this population 1, 4
• Lumbar puncture should be considered in immunocompromised patients, those with fever, or signs of meningeal irritation after head CT 1
• Creatine kinase (CK) levels may help differentiate epileptic seizures from non-epileptic events with high specificity, particularly after generalized tonic-clonic seizures 6

Important Clinical Pitfalls

• Alcohol withdrawal seizures should be a diagnosis of exclusion, especially in first-time seizures in older adults 1, 5
• 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
• 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
• Provoked seizures are common in hospitalized elderly patients, with exposure to proconvulsant drugs being a major risk factor 7
• Non-convulsive status epilepticus should be considered in any older patient with confusion or altered mental status of unclear cause, and EEG should be performed 4

Risk Factors Requiring More Extensive Evaluation

• Abnormal neurological examination or focal deficits 5
• Fever or signs of infection 5
• Immunocompromised status 1
• Recent medication changes, particularly those with known proconvulsant effects 7
• History of malignancy or structural brain lesions 3

Remember that approximately 46% of patients with new-onset seizures require hospital admission, and 95% of those requiring admission can be identified through standardized medical evaluation in the emergency department 8.