Diagnosing Guillain-Barré Syndrome

What to Expect During Your Evaluation

To diagnose Guillain-Barré syndrome (GBS), your healthcare provider may perform several different tests and procedures. The evaluation may include a physical exam, lumbar puncture, electromyography and nerve conduction studies, or blood tests.

Guillain-Barré can be life-threatening and requires close attention by medical professionals, usually in a hospital setting. Here you will find how doctors determine whether a patient has Guillain-Barré syndrome.

Doctor examining a patient
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Physical Exam

Beyond taking a careful history to decide whether Guillain-Barré is a possibility, the doctor will look for certain findings on a physical exam. Because the peripheral nerves are damaged in Guillain-Barré, reflexes, such as the common knee-jerk reflex, are usually absent. The doctor will also test the arms and legs to see if they are weak and do sensory tests to see whether there is any kind of numbness as well. Doctors concerned about Guillain-Barré will pay close attention to the cranial nerves because when these are damaged, it may lead to a need for intubation or mechanical ventilation to ensure that the patient keeps breathing.

Lumbar Puncture

In autoimmune disorders affecting the nervous system, the amount of protein in the body's cerebrospinal fluid (CSF) can be high. For this reason, a lumbar puncture may be performed. Doing a lumbar puncture can also help rule out other potential mimickers of Guillain-Barré, such as infections.

Electromyography and Nerve Conduction Studies (EMG/NCS)

When the peripheral nervous system is afflicted by a disease, it changes the nature of the electrical signals sent and received in that system. By measuring these changes with special equipment, physicians can tell not only whether something is wrong, but also what parts of the nerves are affected most. This information can help guide decisions about treatment options, as well as give the doctor an idea of how severe the illness is and how long it will take someone to recover.

For example, if someone has weakness that is spreading upward like Guillain-Barré can, these electrodiagnostic studies can help determine if the axon or the myelin sheath of the nerve is being attacked. Myelin surrounds the axon and helps electrical signals move faster than they otherwise would. If electricity flows unusually slowly through the nerve, physicians might suspect the myelin is being attacked, in which case the most common form of Guillain-Barré is probably the cause.

On the other hand, if the axon is attacked, less electrical signal will make it through. If this is measured by nerve conduction studies, one of the less common axonal types of Guillain-Barré might be responsible. If this is affecting both sensory and motor neurons, the patient could have acute motor and sensory axonal neuropathy (AMSAN), a more aggressive variant requiring strong treatments and a lot of physical therapy for recovery.

EMG/NCS can be normal early in the course of GBS.

Blood Tests

It is not uncommon for physicians to order blood tests to help diagnose Guillain-Barré syndrome. In some cases, this can help find the antibody responsible. For example, the Miller-Fisher variant of Guillain-Barré is usually associated with an antibody called GQ1b. Finding this antibody confirms a diagnosis of Miller-Fisher variant, and can make the physician especially cautious about a future need for intubation.

Blood tests are also helpful in ruling out other conditions that can appear similar to Guillain-Barré syndrome. Depending on the history and physical exam, the physician may test for signs of cancer, infection, or toxins, such as mercury.

It is important to know exactly what is causing a problem in order to avoid giving improper therapies. Clinching the diagnosis of Guillain-Barré allows medical professionals to focus on proper treatment, and can give you more information about what to expect as the disease progresses, how quickly you will recover, and what kind of assistance you will need to get back on your feet again.

4 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. NIH National Institute of Neurological Disorders and Stroke. Guillain-Barré syndrome fact sheet.

  2. Cleveland Clinic. How is Guillain-Barré syndrome (GBS) diagnosed?

  3. Rocha Cabrero F, Morrison EH. Miller Fisher Syndrome. In: StatPearls [Internet].

  4. National Organization for Rare Disorders. Guillain-Barré syndrome.

Additional Reading
  • Ropper AH, Samuels MA. Adams and Victor's Principles of Neurology, 9th ed: The McGraw-Hill Companies, Inc., McCabe MP, O'Connor EJ.

  • Yuen T. So, Continuum: Peripheral Neuropathies, Immune-Mediated Neuropathies, Volume 18, Number 1.

By Peter Pressman, MD
Peter Pressman, MD, is a board-certified neurologist developing new ways to diagnose and care for people with neurocognitive disorders.