What lab abnormalities are expected in a Basic Metabolic Panel (BMP), Creatine Kinase (CK) level, and prolactin level after a seizure, particularly in a patient with a history of kidney disease, parathyroid disorders, or malnutrition?

Expected Laboratory Abnormalities After Seizure

Serum prolactin elevation is the most reliable laboratory finding after a generalized tonic-clonic seizure, while creatine kinase (CK) elevation occurs commonly with prolonged or repeated seizures, and the basic metabolic panel (BMP) typically shows minimal abnormalities unless predicted by clinical presentation. 1, 2

Prolactin Changes

Generalized Seizures

• Prolactin levels rise significantly within 10-20 minutes after a generalized tonic-clonic seizure and remain elevated for approximately 60-90 minutes before returning to baseline
• This elevation is highly specific for distinguishing true seizures from psychogenic non-epileptic events
• The prolactin rise is most pronounced with generalized convulsive activity

Focal Seizures

• Focal seizures produce inconsistent prolactin elevation, with only some complex partial seizures causing measurable increases
• Simple partial seizures typically do not elevate prolactin levels
• The absence of prolactin elevation does NOT rule out a focal seizure

Special Considerations

• In patients with chronic kidney disease, baseline prolactin levels are already elevated due to reduced renal clearance and increased secretion 3, making post-seizure interpretation challenging
• Timing of the blood draw is critical—samples obtained more than 2 hours post-seizure will likely miss the elevation

Creatine Kinase (CK) Abnormalities

Expected Elevations

• CK rises with prolonged muscle contractions during tonic-clonic activity, typically peaking 24-48 hours after the seizure
• Rhabdomyolysis can develop with severe or repeated seizures, requiring urine dipstick testing for myoglobin 1
• Two patients in one study developed rhabdomyolysis requiring admission 1, highlighting this as a clinically significant complication

Clinical Implications

• Markedly elevated CK (>1000 U/L) warrants aggressive hydration to prevent acute kidney injury
• Serial CK monitoring may be needed if initial levels are significantly elevated
• Muscle pain lasting hours to days after seizure is common 4 and correlates with CK elevation

Basic Metabolic Panel (BMP) Findings

Glucose Abnormalities

• Hypoglycemia and hyperglycemia are the most frequent metabolic abnormalities 1, 2, though usually predicted by history and physical examination
• Post-ictal hyperglycemia from catecholamine surge is common and typically self-resolves
• Prospective studies found only 1-2 cases of unsuspected hypoglycemia per 100-163 patients 1, 5

Sodium Abnormalities

• Hyponatremia is the second most common finding 1, 2, typically in patients with psychogenic water ingestion, diuretic use, or SIADH
• Most cases are clinically apparent from history
• One study found only 1 case of unsuspected hyponatremia in 98 patients 1

Other Electrolytes

• Calcium, magnesium, and phosphate abnormalities are rare in otherwise healthy patients 1
• Testing for calcium and magnesium is indicated in patients with:
  • Known renal insufficiency 1, 2, 5
  • Parathyroid disorders 6
  • Malnutrition 1, 5
  • Diuretic use 1, 5
  • Suspected alcohol-related seizures (check magnesium) 2, 5

Renal Function

• BUN and creatinine are typically normal unless pre-existing kidney disease is present 1
• Post-seizure acute kidney injury can occur with severe rhabdomyolysis
• In chronic kidney disease patients, secondary hyperparathyroidism and vitamin D deficiency are common 7 and may contribute to seizure risk

Practical Testing Algorithm

All Seizure Patients

• Serum glucose and sodium are recommended for all adult seizure patients 2, 5
• Pregnancy test for all women of childbearing age 2, 5
• Consider prolactin level if diagnostic uncertainty exists (must be drawn within 2 hours)

Patients With Risk Factors

• Extended electrolyte panel (calcium, magnesium, phosphate) for:
  • Renal insufficiency 1, 2, 5
  • Malnutrition 1, 5
  • Diuretic therapy 1, 5
  • Known parathyroid disorders 6
  • Alcohol-related seizures 2, 5

Patients With Severe or Repeated Seizures

• CK level and urine dipstick for myoglobin 1
• Serial CK monitoring if initial elevation is significant
• Complete metabolic panel to assess renal function

Critical Pitfalls to Avoid

• Do not order extensive metabolic panels on otherwise healthy patients who have returned to baseline neurological status—the yield is extremely low 1, 5
• Most metabolic abnormalities are predicted by careful history and physical examination 1, 2
• Prolactin testing is only useful if drawn within 2 hours of the seizure and should not be relied upon for focal seizures
• In patients with chronic kidney disease, baseline prolactin elevation 3 and altered mineral metabolism 8, 7 complicate interpretation of post-seizure labs
• Alcohol withdrawal seizures should be a diagnosis of exclusion 2, 5, 4, especially in first-time seizures—check magnesium levels in this population