Tests and diagnosis

By Mayo Clinic Staff

Because people in coma can't express themselves, doctors must rely on physical clues and information provided by families and friends. Be prepared to provide information about the affected person, including:

  • Events leading up to the coma, such as vomiting or headaches
  • Details about how the affected person lost consciousness, including whether it occurred suddenly or over time
  • Any noticeable signs or symptoms prior to losing consciousness
  • The affected person's medical history, including other conditions he or she may have had in the past, such as stroke or transient ischemic attacks
  • Recent changes in the affected person's health or behavior
  • The affected person's drug use, including prescription and over-the-counter medications as well as unapproved medications or illegal, recreational drugs

Physical exam

In a physical exam, doctors will check the affected person's movements and reflexes, response to painful stimuli, and pupil size. Doctors will observe breathing patterns to help diagnose the cause of coma. Doctors also may check the skin for signs of any bruises due to trauma.

To determine the affected person's level of consciousness, doctors may speak loudly or press on the angle of the jaw or nail bed. Doctors will watch for signs of arousal, such as vocal noises, eyes opening or movement.

Doctors will test reflexive eye movements. These tests can help determine the cause of coma and the location of brain damage.

Doctors may also squirt ice-cold or warm water into the affected person's ear canals and observe eye reactions.

Laboratory tests

Blood samples will be taken to check for:

  • Complete blood count
  • Electrolytes, glucose, thyroid and liver function
  • Carbon monoxide poisoning
  • Drug or alcohol overdose

A spinal tap (lumbar puncture) can check for signs of infections in the nervous system. During a spinal tap, a doctor or specialist inserts a needle into the spinal canal and collects a small amount of fluid for analysis.

Brain scans

Imaging tests help doctors pinpoint areas of brain injury. Tests may include:

  • Computerized tomography (CT scan). A CT scan uses a series of X-rays to create a detailed image of the brain. A CT scan can show a brain hemorrhage, tumors, strokes and other conditions. This test is often used to diagnose and determine the cause of coma.
  • Magnetic resonance imaging (MRI). An MRI uses powerful radio waves and magnets to create a detailed view of the brain. An MRI can detect brain tissue damaged by an ischemic stroke, brain hemorrhages and other conditions. MRI scans are particularly useful for examining the brainstem and deep brain structures.
  • Electroencephalography (EEG). An EEG measures the electrical activity inside the brain. Doctors attach small electrodes to the scalp. Doctors send a low electrical current through the electrodes. The brain's electrical impulses are then recorded. This test can determine if seizures may be the cause of coma.
Oct. 12, 2012

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