Can a seizure occur during a blood draw?

Can Seizures Occur During Blood Draw?

Yes, seizures can occur during a blood draw, but they are extremely rare and typically represent either vasovagal syncope with convulsive movements (not a true seizure) or an underlying seizure disorder coincidentally triggered during the procedure.

Understanding the Distinction

The key issue is differentiating true epileptic seizures from syncope with convulsive-like movements:

• Vasovagal syncope during blood draws is common and may include brief tonic-clonic movements that mimic seizures, but these are not true epileptic events 1
• True seizures are uncontrolled electrical discharges of neurons in the brain that can occur due to infections, trauma, metabolic abnormalities (hypoglycemia), or underlying neurological conditions 1
• Tonic-clonic movements in syncope are always brief (<15 seconds) and start after loss of consciousness, whereas true seizure movements are prolonged and coincide with loss of consciousness 1

Clinical Evidence from Blood Donation Studies

A large-scale study of blood donors with known seizure disorders provides reassuring data:

• Among 723 blood donations from 613 individuals with a history of seizures, the adverse reaction rate was only 3.34% (not significantly different from the general donor population at 2.24%) 2
• The risk of syncope with or without convulsive activity was extremely low (0.21%) in people with seizures versus 0.28% in other donors 2
• Even among donors taking antiepileptic medications (25.7%) or those with recent seizures in the preceding year (8.4%), no significant increase in adverse reactions occurred 2

Potential Mechanisms for Seizures During Blood Draw

If a true seizure occurs during phlebotomy, consider these precipitating factors:

• Vasovagal response causing cerebral hypoperfusion in susceptible individuals 1
• Acute metabolic disturbances such as hypoglycemia, which can trigger seizures 1, 3
• Anxiety or hyperventilation in patients with underlying seizure disorders 4
• Pre-existing epilepsy where the procedure coincidentally occurs during a seizure 4
• Medication effects or withdrawal states 3

Distinguishing True Seizures from Syncope

Critical clinical features to assess:

• Before the event: True seizures may have an aura (rising abdominal sensation, unusual smell), while syncope presents with nausea, lightheadedness, and blurred vision 1
• During the event: Seizure movements are prolonged and begin with loss of consciousness; syncope movements are brief (<15 seconds) and occur after consciousness is lost 1
• Tongue biting: Occurs on the side of the tongue in epilepsy versus the tip in syncope 1
• Post-event: Prolonged confusion suggests seizure; rapid return to baseline suggests syncope 1
• Pallor and sweating: Common in syncope, uncommon in epilepsy 1

Immediate Management

If a seizure-like event occurs during blood draw:

• Stop the procedure immediately and ensure patient safety by helping them to the ground if not already supine 1
• Place the patient on their side in the recovery position to protect the airway 1
• Clear the area around the patient to minimize injury risk 1
• Stay with the patient and monitor vital signs 1
• Do NOT restrain the patient or place anything in their mouth 1

When to Activate Emergency Services

Call EMS for:

• First-time seizure occurrence 1
• Seizures lasting >5 minutes 1
• Multiple seizures without return to baseline mental status between episodes 1
• Seizures with traumatic injuries, difficulty breathing, or choking 1
• Failure to return to baseline within 5-10 minutes after seizure activity stops 1

Risk Stratification

Patients at higher risk for true seizures during procedures include those with:

• Known epilepsy or seizure disorders 4
• Recent brain injury or stroke 5
• Metabolic abnormalities (hypoglycemia, electrolyte imbalances) 3, 6
• Medication withdrawal states (especially alcohol or benzodiazepines) 3, 5
• Acute systemic illness 3

Common Pitfalls to Avoid

• Do not assume all convulsive movements during blood draw are true seizures; most are brief convulsive syncope 1
• Do not administer anticonvulsants for simple vasovagal syncope with brief movements 1
• Do not restrict patients with well-controlled epilepsy from blood donation, as evidence shows they are not at increased risk 2
• Do not place objects in the mouth of someone having a seizure, as this can cause injury 1