A seizure is a sudden, uncontrolled electrical disturbance in the brain that temporarily affects a person’s movement, behavior, or consciousness. When an individual experiences a suspected seizure, especially a first one or one with associated injury, medical providers quickly order blood tests in the emergency setting. These laboratory tests serve two main purposes: confirming that an epileptic event occurred and, more importantly, identifying any underlying medical conditions that may have triggered the episode. The focus shifts from the brain event itself to the physical and chemical changes it causes in the body, which can be measured through specific biomarkers.
Prolactin The Post-Seizure Indicator
The hormone prolactin is one of the most specific laboratory markers used to help confirm a generalized epileptic seizure. Prolactin is released by the pituitary gland, and its secretion is heavily influenced by the brain’s electrical activity. During a generalized tonic-clonic seizure, the intense electrical discharge spreads to the hypothalamus, triggering a massive surge of prolactin release into the bloodstream.
This surge is rapid, with prolactin levels typically peaking in the blood within 10 to 20 minutes after the seizure ends. Levels often rise to three or four times the normal baseline level. This quick increase is useful in distinguishing true generalized epileptic seizures from events that mimic them, such as psychogenic non-epileptic seizures or fainting (syncope).
The clinical utility of this test depends heavily on timing because the elevated levels are transient. Prolactin typically returns to baseline levels within 60 to 100 minutes post-seizure. Therefore, a blood sample must be drawn quickly after the event to capture the peak elevation. If the sample is taken too late, the result may be falsely negative.
Lactic Acid and Creatine Kinase Indicators
Two other markers that become significantly elevated after a generalized seizure reflect the immense physical strain placed on the body during the event. These are lactic acid and creatine kinase, which are direct consequences of the violent, uncontrolled muscle activity known as convulsions. Muscle exertion during a tonic-clonic seizure leads to a temporary state of anaerobic metabolism, where the muscles demand more oxygen than the body can supply.
Lactic acid, or lactate, is the byproduct of this anaerobic energy production and rapidly spikes in the blood immediately following the seizure. Levels sometimes increase more than eightfold within minutes of the event, making this elevation a reliable marker for generalized tonic-clonic seizures. This immediate elevation is temporary, with levels normalizing back to baseline within two hours as the body restores its oxygen balance.
Creatine kinase (CK) is an enzyme released into the bloodstream due to the sheer force of muscle contraction during a generalized seizure. Higher levels indicate greater muscle breakdown as the enzyme leaks out of damaged muscle cells. While lactate is an immediate marker, CK elevation is delayed, typically peaking 24 to 48 hours after the seizure event. Because of this delayed peak, a follow-up measurement the next day may reveal a significant elevation proportional to the duration and intensity of the seizure activity.
Blood Chemistry Screens for Underlying Causes
Beyond the markers that confirm the event, a comprehensive blood chemistry screen is performed to identify underlying medical conditions that could have caused the seizure. Blood glucose is checked, as dangerously low blood sugar (hypoglycemia) is a major, rapidly reversible cause of seizures. Prompt identification and treatment of hypoglycemia are necessary for patient safety.
Electrolyte imbalances are a frequent cause of seizures, particularly low sodium levels (hyponatremia). Sodium is essential for the proper electrical signaling of brain cells, and an abnormal concentration can disrupt function and trigger uncontrolled firing. The metabolic panel also assesses kidney and liver function through tests like blood urea nitrogen (BUN) and creatinine, since dysfunction in these organs can lead to systemic illness that precipitates a seizure.
A toxicology screen is also performed to check for the presence of drugs or alcohol. Seizures can be caused by substance overdose, toxic exposure, or withdrawal from certain medications or recreational drugs. Identifying these external factors is a necessary step in determining the cause of the event and guiding the appropriate management plan.
How Timing Affects Lab Results
The laboratory investigation of a seizure is highly dependent on timing, as the interpretation of many results hinges on the interval between the seizure’s end and the blood draw. The rapid, transient nature of prolactin and lactate elevations means they are only reliable biomarkers if sampled within a narrow window. A delay of just a few hours can result in these levels returning to baseline, obscuring evidence of a generalized seizure.
Conversely, creatine kinase (CK) elevation is a delayed phenomenon, requiring a follow-up blood draw hours later to capture its peak. If only an initial blood sample is taken, the CK level may be falsely low, missing the sign of significant muscle damage. This contrast highlights that prolactin and lactate mark the immediate event, while CK indicates the physical aftermath.
The timing of the blood draw is less critical for metabolic and toxicology screens, which look for underlying causes rather than the event itself. Glucose and electrolyte values provide a snapshot of the body’s internal environment, indicating potential triggers like hyponatremia or hypoglycemia. Understanding the different time courses of these biomarkers is necessary for medical providers to accurately interpret the lab results and diagnose the patient’s condition.