Currently, there is no test that can definitively diagnose Guillain-Barré syndrome (GBS). Patients who suspect they may have GBS or another neurological condition may be referred to a neurologist for diagnosis and treatment.

A physician who suspects GBS will likely begin by compiling a medical history of the patient. The physician may ask questions such as whether the patient has recently experienced any type of respiratory or gastrointestinal illness. The patient’s symptoms will be discussed, including whether certain symptoms (e.g., tingling sensations, weakness, paralysis) are affecting both sides of the body, whether symptoms are worsening or spreading to other areas of the body and how quickly this is occurring. If a fever is present, it may indicate another medical condition instead of GBS.

A physician will also perform a complete physical examination of the patient. This examination may include a blood pressure reading and heart rate check. A knee-jerk reflex test may be performed to look for diminishment or absence of this reflex, which may indicate nerve conduction problems and GBS.

In previous years, the muscle weakness and inability to move of GBS had to be distinguished from polio, another condition that affects the nervous system and may cause paralysis. However, polio has been essentially eradicated in developed countries, making GBS the most common condition with flaccid paralysis of the muscles.

In addition, signs and symptoms of GBS may vary considerably from person to person. This makes an accurate diagnosis more difficult.

Diagnostic tests that may be used when GBS is suspected include:

• Electromyography (EMG). Measures the electrical activity of a muscle in response to nerve stimulation. This test involves inserting fine needles that contain electrodes into muscles and placing electrodes on the skin over peripheral nerves.
  
  
  Nerve conduction velocity (NCV) test. Typically performed along with an EMG. This test measures the speed of signals that travel through the nerves.
  
  
• Spinal tap (lumbar puncture). Determines the pressure of cerebrospinal fluid (CSF), a clear fluid that bathes and protects the brain and spinal cord. A needle is inserted into the spinal canal and a sample of fluid is removed for laboratory analysis. Spinal taps can help find evidence of bleeding, determine the number and types of white blood cells (WBC) that are present, determine levels of glucose and levels and types of protein, and test for bacteria and fungi. Elevated levels of protein in the CSF are associated with GBS, although this may not be detected during the first week of illness. Other diseases may also cause an elevated rise in CSF protein levels.

If Miller Fisher syndrome (a form of GBS) is suspected, blood tests may be performed to detect the presence of certain antibodies that are typically present in patients with MFS. A nerve biopsy may be required to identify a similar but different condition called chronic inflammatory demyelinating polyneuropathy.

Blood tests and imaging tests may also be used to rule out other possible causes of the patient’s symptoms. Urine tests may help rule out heavy metal poisoning as the cause of symptoms.