Diagnosis

Because people in a 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
• Noticeable signs or symptoms before losing consciousness
• The affected person's medical history, including other conditions he or she may have had in the past, such as a 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 and illicit recreational drugs

Physical exam

The exam is likely to include:

• Checking the affected person's movements and reflexes, response to painful stimuli, and pupil size
• Observing breathing patterns to help diagnose the cause of the coma
• Checking the skin for signs of bruises due to trauma
• Speaking loudly or pressing on the angle of the jaw or nail bed while watching for signs of arousal, such as vocal noises, eyes opening or movement
• Testing reflexive eye movements to help determine the cause of the coma and the location of brain damage
• Squirting cold or warm into the affected person's ear canals and observing eye reactions

Laboratory tests

Blood samples will be taken to check for:

• Complete blood count
• Electrolytes, glucose, thyroid, kidney 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 might include:

• CT scan. This 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 a coma.
• MRI. This 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). This measures the electrical activity inside the brain through small electrodes attached to the scalp. Doctors send a low electrical current through the electrodes, which record the brain's electrical impulses. This test can determine if seizures might be the cause of a coma.