Which laboratory values are typically elevated after a seizure?

Laboratory Values Elevated After a Seizure

Lactate, ammonia, prolactin, and creatine kinase are the laboratory values most commonly elevated after a seizure, with lactate being the most robust marker—rising in approximately 90% of cases within 30 minutes of seizure termination.

Most Reliable Post-Seizure Markers

Lactate (Most Sensitive)

• Lactate levels increase approximately 8.7-fold above baseline immediately after tonic-clonic seizures, with elevations more than twice the upper limit of normal in 90% of cases 1
• Levels return to baseline within 2 hours of seizure termination 1
• Postictal lactate levels correlate significantly with the total duration of the tonic-clonic phase 1
• This makes lactate the single most reliable metabolic marker for confirming recent seizure activity 1

Ammonia

• Ammonia levels rise approximately 2.6-fold after tonic-clonic seizures, with elevations above twice the upper limit of normal in 71% of cases 1
• Like lactate, ammonia returns to baseline within 2 hours 1
• Ammonia has diagnostic potential as a postictal blood test marker 2

Prolactin

• Prolactin increases approximately 5.1-fold after seizures, with elevations in 70% of tonic-clonic seizures 1
• Prolactin testing helps differentiate epileptic seizures from psychogenic non-epileptic seizures in adults and adolescents, with high specificity and moderate sensitivity 2
• Levels normalize within 2 hours post-seizure 1

Creatine Kinase (CK)

• CK elevations are common after generalized tonic-clonic seizures but occur with a delayed time course—peaking at 48 hours rather than immediately 1
• CK was elevated in only ~10% of video-EEG-documented tonic-clonic seizures in one study, challenging its value as an immediate diagnostic marker 1
• However, other studies found CK increased in 59.4% of patients after generalized tonic-clonic seizures 3
• CK displays high specificity and moderate sensitivity for generalized tonic-clonic seizures 2
• Rhabdomyolysis with >50-fold CK elevation occurs in approximately 1.9% of patients 3

Electrolyte Disturbances

Phosphate

• Hyperphosphatemia occurs in one-third of patients immediately after tonic-clonic seizures 1
• Hypophosphatemia develops in one-third of patients 2 hours after seizure termination 1
• This biphasic pattern is characteristic of the metabolic stress response to seizures 1

Other Electrolytes

• Subtle but significant alterations occur in sodium, potassium, and other electrolytes after tonic-clonic seizures 1
• Creatinine and uric acid levels also show mild elevations 1

Cardiac Markers

Troponin I

• Troponin I elevations occur in 12% of patients after generalized tonic-clonic seizures, with occurrence significantly correlated with patient age 3
• Troponin should be measured when cardiac complications are suspected, particularly in older patients 3
• Myocardial infarction (NSTEMI or STEMI) occurs in <1% of cases but must be excluded when troponin is elevated 3

Glucose

• Glucose levels are moderately increased after tonic-clonic seizures 1
• However, hypoglycemia is one of the most important treatable causes of seizures and must be checked immediately in all seizure patients 4, 5

Clinical Context: When to Order These Tests

For Diagnostic Confirmation

• In patients with suspected but unwitnessed seizures, lactate measured within 30 minutes provides the highest diagnostic yield 1
• Prolactin and ammonia offer additional diagnostic support when measured within 2 hours 1
• CK is less useful for immediate diagnosis but may help retrospectively if measured 24-48 hours after the event 1, 3

For Identifying Seizure Etiology

• The American College of Emergency Physicians recommends that only serum glucose and sodium should be routinely measured in otherwise healthy adults who have returned to baseline, as these are the only tests that consistently alter acute management 6, 4, 5
• Glucose abnormalities and hyponatremia are the most frequent metabolic causes of seizures and are usually predicted by history and physical examination 6
• Additional metabolic panels (calcium, magnesium, phosphate) should be ordered only when clinical clues such as vomiting, diarrhea, dehydration, known renal disease, or malignancy are present 4, 5

For Detecting Complications

• CK, electrolytes, creatinine, and liver and renal function tests should be measured on at least one occasion to identify patients at risk for rhabdomyolysis, acute renal failure, or cardiomyopathy 2
• Troponin should be checked in older patients and those with cardiac risk factors 3

Important Caveats

• No postictal laboratory value can definitively prove or rule out the diagnosis of an epileptic seizure 2
• The clinical examination successfully predicts laboratory abnormalities in the vast majority of cases 7
• Routine extensive laboratory workups in patients who have returned to baseline neurologic status have extremely low yield 6, 7, 8
• In one prospective study of 136 patients with new-onset seizures, only 2 cases of hypoglycemia were not suspected based on history and physical examination 8