The Glasgow Coma Scale: Definition, Use, and Advantages

The Glasgow Coma Scale: Definition, Use, and Advantages

Last update: 04 October, 2018

The Glasgow Coma Scale (GCS) is a neurological evaluation tool that physicians use to evaluate the level of consciousness of a person with brain damage. It allows us to explore or quantify three parameters or criteria for observation. They are 1) eye response, 2) verbal response, and 3) motor response.

The Glasgow Coma Scale is the most used tool in hospital and pre-hospital environments. Some of the advantages of the GCS is that it’s easy to use and it facilitates a common language and objective. That, in turn, makes communication between healthcare professionals much easier.

What is the Glasgow Coma Scale?

The Glasgow Coma Scale was designed in 1974 by two English neuroscientists named Bryan Jennett and Graham Teasdale. They were members of the Institute of Neuroscience & Psychology. They published the first version of this scale in The Lancet magazine. Their article was titled Assessment of Coma and Impaired Consciousness.

A doctor evaluating patient using the Glasgow Coma Scale.

In the 60s, Jennet created a database with all of the patients he saw in Glasgow with traumatic brain injury (TBI). His collaborators in the Netherlands and the United States did the same thing. This database became the foundation upon which he and his colleague created the Glasgow Coma Scale.

Little by little, it became a key tool to objectively evaluate the level of consciousness in patients who suffered from a traumatic brain injury. It was divided into three categories that individually evaluated three aspects of consciousness: eye response, verbal response, and motor response. The sum total of all the points was fourteen.

The addition of one more point

The final version of the scale was created two years later, in 1976. They decided to add a new point to evaluate decerebrate posture, a sign of serious brain damage. This is an abnormal body posture where the arms are bent towards the body, the hands are in tight fists, and the legs are very straight. The entire body is stiff and rigid.

The three sub-scales remained, but this addition brought the total points from 14 to 15The total today is still 15. 


Initially, the Glasgow Coma Scale was created to estimate the severity of traumatic brain injury. These days, doctors use it to evaluate less serious altered levels of consciousness in post-traumatic situations. They also use it for things like the depth and duration of a coma.

When someone suffers a blow to the head, doctors have to examine them as quickly as possible. The neurological evaluation should be simple, objective, and fast. The most important aspect to keep in mind is the level of consciousness. Consequently, in these cases, the GCS is crucial. The patient’s score on the scale helps us understand the severity of the injury.

On the other hand, it also helps identify states of coma and see their evolution. Doctors can use the scale longitudinally (over the course of time) to understand the fluctuations in these changes.

Score and interpretation

Doctors evaluate each of the three aspects and give points for the best response in each category. The lowest possible score is 3 (1+1+1) and the highest is 15 (4+5+6). Healthcare professionals determine the severity of TBI using this score and Gennarelli’s classification:

  • Mild: 14-15 points
  • Moderate: 9-13 points
  • Severe: <9 points

In terms of the altered level of consciousness (state of coma) the gradient varies:

  • Mild: >13 points. The duration of the coma tends to be less than 20 minutes.
  • Moderate: 9-12 points. The duration of the coma is greater than 20 minutes but less than 6 hours after the patient was admitted.
  • Serious or severe: <8 points. The coma’s duration is longer than 6 hours after the patient was admitted.
Woman in a coma suspended in the air.

Advantages of the Glasgow Coma Scale

When it comes to health, the more precise we can be with the terms and concepts that we use, the better. That’s why the Glasgow Coma Scale is so useful. It allows providers to avoid ambiguities like “the patient is drowsy, unconscious, or comatose”. We can also be more exact about the clinical state and evolution of the patient. The Glasgow Coma Scale gives providers precision and certainty. 

In addition, the precision and relative simplicity of this scale make it universally popular. Experts use it for other traumatic and non-traumatic pathologies. Professionals in diverse fields use it for emergency situations.

The GCS is a complete tool that evaluates three key aspects. The best part of all is that healthcare professionals can use it again and again. This scale offers longitudinal information about the evolution of a coma. Consequently, it’s very useful in the early stages of treatment.

All cited sources were thoroughly reviewed by our team to ensure their quality, reliability, currency, and validity. The bibliography of this article was considered reliable and of academic or scientific accuracy.

  • ASSESSMENT OF COMA AND IMPAIRED CONSCIOUSNESS. A Practical Scale. Teasdale, Graham; Jennett, Bryan. The Lancet. 1974.

This text is provided for informational purposes only and does not replace consultation with a professional. If in doubt, consult your specialist.