Glasgow Coma Scale (GCS)

What is the Glasgow Coma Scale?

The Glasgow Coma Scale (GCS) is a system to “score” or measure how conscious you are. It does that by giving numbered scores for how awake you are, your level of awareness and how you respond to basic instructions.

Experts at the University of Glasgow in Scotland developed the GCS in 1974. Despite “coma” being part of the name, the GCS sees much wider use in medicine today. It’s the most commonly used scale for measuring decreases in consciousness, including coma.

What is consciousness?

In the medical context, consciousness has three requirements. To be conscious, you have to be:

• Awake: This includes whether or not you have the ability to wake up because of voice or touch. That’s what makes a coma different from just being asleep.
• Alert: This is how responsive you are to people talking to you and if you’re able to understand what’s happening in your immediate surroundings.
• Oriented: This means you know who you are, where you’re at, what day it is and other details related to the here and now.

When is the Glasgow Coma Scale used?

Healthcare providers can use the GCS as part of a neurological exam. It’s also useful for any situation where you might have a decrease in how conscious you are. That includes injury-related conditions like concussions and traumatic brain injuries.

The scale also can help with conditions that don’t involve injuries, such as low blood sugar (hypoglycemia), poisoning or after a seizure.

What does the Glasgow Coma Scale measure?

A neurological exam looks for any problems with the function of the two main parts of your nervous system. Those parts are your:

• Central nervous system: This consists of your brain, brainstem, optic nerves (these link your brain to the retinas at the back of your eyes) and spinal cord.
• Peripheral nervous system: This is all the nerves outside of your central nervous system.

The Glasgow Coma Scale has three categories that apply to a neurological exam. Most of them apply to your brain itself, but some can also involve your spinal cord and nerves throughout your body:

• Eye response: This relates to how awake and alert you are.
• Motor response: This part is about how well your brain can control muscle movement. It can also show if there are any issues with the connections between your brain and the rest of your body.
• Verbal response: This tests how well certain brain abilities work, including thinking, memory, attention span and awareness of your surroundings.

How does the Glasgow Coma Scale work?

To get your Glasgow Coma Scale score, providers take the scores from the three categories of the GCS and add them together. A healthcare provider will test each of the three categories in multiple ways. An example of this is testing your verbal response by asking you a few different questions, such as what day of the week or date it is or what city you're in currently.

One of the best uses of the GCS is to track changes in your level of consciousness. Healthcare providers will often repeat a neurological exam at regular intervals to check for and document any changes in your GCS score.

The scoring guidelines for the categories are as follows:

Eye response

This is mainly about how awake you are. If you’re unconscious, it measures the level of unconsciousness by testing reflex responses to pressure. Pressure here means something like a pinch or a poke. It should be just enough to cause minor, momentary discomfort but not injury.

Verbal response

A provider checks this by asking you questions that test your memory, thinking ability and your awareness of the world around you. Your provider can also use this to see if there are any brain or nerve problems affecting control of your face and mouth.

Motor response

This part can reveal any issues with the connections between your nerves, spinal cord and brain. It also tests your brain’s ability to control muscle movement and how well you can understand and follow instructions.

GCS-P

In 2018, a team of experts — including one of the original creators of the GCS — published an updated version of the GCS called the “GCS-P.” The P stands for “pupil,” as in the pupil of the eye. This is a fourth number that providers subtract from the standard GCS score.

Pupil reaction is important because it’s an indicator of your brain function. When your pupils don’t react to light, it’s a sign that a serious problem or injury is affecting your brain. The pupil score ranges from 0 to 2.

The pupil scores mean:

• 2: Neither pupil reacts to light.
• 1: One pupil doesn’t react to light.
• 0: Both pupils react to light.

Subtracting the pupil reaction score from the GCS score means that the GCS-P score can range from 1 to 15. The GCS-P score still uses a score of 8 or fewer to mean a coma.

A GCS score of 3 and a pupil score of 2 is a GCS-P score of 1. That means a very deep coma and no pupil reaction in both eyes.

Does a neurological exam that uses the Glasgow Coma Scale involve pain?

Older descriptions of the GCS use the word “pain” to describe the sensation used to test certain reflexes. Newer guidelines change that word to “pressure.” The word change is more accurate because it doesn’t involve an injury. It’s also clearer because a provider isn’t actually trying to cause pain or hurt your loved one.

The original GCS guidelines were also vague on where providers should press to test reflexes. In 1975, a year after the original publication of the GCS, the experts who created the GCS published specific guidance. Points where a provider will put pressure include your:

• Nail beds: Your fingernails and toenails are pressure-sensitive. Providers often push on one or more of them during a neurological exam to test if your body reacts reflexively to the pressure.
• Trapezius muscle: This muscle connects your shoulder to the center of your neck and back. It’s an easy-to-reach muscle to check for a pressure reflex.
• Supraorbital notch: This is a small groove in the bone of your skull just above your eye and just below your eyebrow.

What type of results do you get, and what do the results mean?

The highest possible GCS score is 15, and the lowest is 3. A score of 15 means you’re fully awake, responsive and have no problems with thinking ability or memory. Generally, having a score of 8 or fewer means you’re in a coma. The lower the score, the deeper the coma is.

Healthcare providers may abbreviate your GCS score using letter/number combinations. A score of 15 would be “E4V5M6.” A score of 3 would be “E1V1M1.”

GCS ranges for head injuries

When providers use the GCS in connection with a head injury, they tend to apply scoring ranges to describe how severe the injury is. The ranges are:

• 13 to 15: Mild traumatic brain injury (mTBI). Also known as a concussion.
• 9 to 12: Moderate TBI.
• 3 to 8: Severe TBI.

What should I know about my loved one’s GCS score?

Generally, your family or close loved ones will be the ones to talk to your healthcare provider about your score(s). Some things you should know about the GCS and how healthcare providers use it include:

• The results of the test are much more complex than just a number. A GCS score doesn’t include details about the results of the test. There’s a lot more to a neurological exam than just a number. While the number is generally easier to understand, it’s best to talk to your loved one’s provider to understand your loved one’s condition better.
• The GCS has its limits. It may not be possible to use the GCS in some situations, such as when someone is on a ventilator or doesn’t speak the same language as their healthcare provider. It also isn’t useful for people with conditions or injuries affecting body parts or systems the GCS relies on, such as vision or hearing loss.
• The GCS isn’t the only thing providers use to make a prognosis. Healthcare providers commonly use the GCS to predict likely outcomes, but it isn’t the only factor they consider. Ask your loved one’s provider about the score and what it might mean long term.

A note from Cleveland Clinic

The Glasgow Coma Scale is the most common tool healthcare providers use to measure decreases in consciousness and comas. Since its creation almost 50 years ago, experts have studied the scale extensively and found that it continues to be a useful diagnostic tool. (They’ve even improved it along the way.) Using this tool also helps providers track changes in brain function. That helps guide treatment and improve care for people with conditions that affect their level of consciousness.