Diagnosis of Febrile SeizuresM

When a febrile seizure occurs, parents and caregivers should contact the child's pediatrician immediately. Diagnosis may involve a history of symptoms and a thorough physical examination, including a neurological exam.

In some cases, laboratory tests (e.g., blood tests, urine tests, lumbar puncture) are performed to rule out other possible causes for the seizure, such as dehydration (e.g., caused by severe vomiting and/or diarrhea) and meningitis and determine the cause for the fever.

Blood tests that may be performed include a complete blood count (CBC) and blood cultures. These tests are used to detect viruses or bacteria and high levels of white blood cells, which may indicate infection.

In some cases, a lumbar puncture (also called a spinal tap) is performed to rule out meningitis. In this test, a needle inserted between two lumbar vertebrae in the spinal column is used to withdraw cerebrospinal fluid for microscopic evaluation. The fluid is examined for pathogens (e.g., virus, bacteria) and elevated levels of white blood cells. Cerebrospinal fluid also may be cultured to identify the virus or bacterium.

Further testing may not be needed if the child is developmentally normal, if the results of the neurological exam are normal, and if the febrile seizure meets the following criteria:

  • Seizure is general, not focal (i.e., involves more than one part of the body).
  • Seizure does not last longer than 15 minutes.
  • Seizure does not recur within 24 hours.

Complex febrile seizures may require more extensive diagnostic testing. If the results of the physical examination and laboratory tests are inconclusive, or if the physician suspects a neurological condition, such as epilepsy, an electroencephalogram (EEG) may be performed.

EEG is a noninvasive test that detects, measures, and records brain wave activity. In this test, electrodes are placed on the head and attached by wires to a machine that converts electrical signals from the brain into wavy lines on a moving sheet of graph paper. Electroencephalogram usually is performed about 1 week after a febrile seizure because high fever or the seizure itself can affect the results.

Publication Review By: Stanley J. Swierzewski, III, M.D.

Published: 27 Aug 2008

Last Modified: 15 Sep 2015