Glasgow Coma Scale: Definition When to use? How to calculate the score? Limitations and Reliability

Designed in 1974, it is a tool that has the ability to communicate the level of awareness of patients with acute or traumatic brain injury.

Developed by Graham Teasdale and Bryan J. Jennett , professors of neurosurgery at the Institute of Neurological Sciences at the University of Glasgow, this scale is the gold standard used for all acute medical and trauma patients.

The most widely used methods to describe traumatic brain injury (TBI) are the Glasgow Coma scale (GCS) and the abbreviated scale of injury (AIS).

Recent evidence suggests that the presentation of the Glasgow coma scale in elderly patients may be higher than in younger patients with an equivalent anatomical severity of traumatic brain injury.

Used by trained medical professionals, the Glasgow coma scale is an objective and reliable tool that nurses and nursing students should become familiar with, regardless of where they work.

Most commonly used in the intensive care unit and in the emergency room, nurses may need to perform a Glasgow coma scale on a patient at any time.

The Glasgow coma scale, which can identify changes in consciousness in patients with traumatic brain injuries, is a tool that requires nurses to fully understand their purpose and how to use it.

Identifying patients who need a score is the first step in correctly using the scale.

Population expected to use the Glasgow coma scale

The Glasgow coma scale was originally developed to help determine the severity of a coma or dysfunction after a traumatic brain injury, but it can be useful for any condition that leads to an alteration of consciousness.

Today, it is used systematically for many conditions, including stroke (subarachnoid hemorrhage, intracerebral hemorrhage or ischemic stroke), infection, seizures, brain abscess, general traumas, non-traumatic coma, overdose and poisoning.

It can also be administered in a variety of settings, such as prehospital, arrival at the emergency department and in the hours after admission, which allows you to control changes and trends in the patient’s consciousness over time.

Modified scales have been developed for use in other populations. The Glasgow Coma Scale – Extended (GCS-E) includes the use of an amnesia scale to prevent premature discharge of patients with mild traumatic brain injury.

The scales developed for use in the pediatric population have also been modified. The motor scale has proved to be the most useful for evaluation in both older and preverbal children when studying closed traumas.

When to use?

Patients who need an assessment of the Glasgow coma scale have usually suffered traumatic brain injury and are in the emergency room or intensive care unit.

The Glasgow comma scale should be performed at the time of admission and then every four hours unless otherwise indicated by the medical team.

The documentation of the Glasgow coma scale is crucial since the medical team, which usually includes neurology, will use this to determine the improvement or decompensation of the patient.

How to calculate the score

The Glasgow coma scale analyzes patients according to three different criteria:

  • Opening of eyes
  • Motor response
  • Verbal response

Each criterion is on a different scale with a possible total score of 15. The lowest possible score is 3.

Eye response:

  • Closed by local factor – (NT).
  • None: No opening at any time, no interference factor (+1).
  • Pressure: After the stimulation of the fingertip (+2).
  • To the sound: After the spoken request (+3).
  • Spontaneous: Open before the stimulus (+4).

Verbal response:

  • Not verifiable: Factor that interferes with communication (NT).
  • None: No audible response, no interfering factor (+1).
  • Sounds: Only moans / moans (+2).
  • Words: intelligible individual words (+3).
  • Confused: Not oriented, but communicates consistently (+4).
  • Oriented : Indicates correctly the name, place and date (+5).

Motor response:

  • Not verifiable: Paralyzed or other limiting factor (NT).
  • None: No movement in arms / legs, no interfering factor (+1).
  • Extension: Extend the arm to the elbow (+2).
  • Abnormal Flexion: Flexes the arm at the elbow, presents a predominantly abnormal characteristic (+3).
  • Normal flexion: Folds the arm at the elbow quickly but does not present a predominantly abnormal appearance (+4).
  • Location: Brings the hand over the clavicle to a stimulus in the head / neck (+5)
  • Obeys Commands: 2 part request (+6).

Medical professionals use the aforementioned scale to obtain the best eye opening response, the best motor response and the best verbal response. Patients with tracheostomy and endotracheal breathing tubes are considered.

The 1t column is added to the verbal response in some hospitals to accommodate those patients without altering their Glasgow coma scale score.

To calculate a patient’s Glasgow coma scale, first rate the patient in each of the three main areas.

Once a number has been determined, add theses to create the sum that is the patient’s Glasgow score. Once a score has been identified, it is important to understand the meaning.

Each brain injury is different, but in general, the brain injury is classified as:

Serious : Glasgow coma scale of 3-8.

Moderate : Glasgow coma scale of 9-12.

Mild : Glasgow coma scale of 13-15.

As mentioned above, the adaptations are made for intubated patients, but also for those with severe facial edema or swelling. These patients are identified with the numerical value of 1 and an adjunct modifier.

For example, an intubated patient would have a verbal response of 1t, whereas a patient with pronounced ocular swelling would have an ocular response of 1c that would identify the eyes as closed and unable to open due to swelling.


While the Glasgow coma scale is a great diagnostic tool, there are multiple limitations that can alter the score and not provide an accurate picture of the patient’s brain injury. These include:

  • Pre-existing facts.
  • Language or cultural difference.
  • Loss of hearing or speech impediment.
  • Intellectual or basal neurological deficit.
  • Basal psychological problems.
  • Age (real and intellectual).
  • Current treatment
  • Physical.
  • Intubation
  • Edema (swelling)
  • Traqueostomía .
  • Pharmacological.
  • Sedation.
  • Paralysis.
  • Other injuries / injuries / injuries.
  • Fractura orbital.
  • Cranial fracture
  • Damage to the spinal cord
  • Dysphasia (language disorder due to brain damage).
  • Hemiplegia (paralysis of one side of the body).
  • External factors.
  • Alcohol.
  • Drugs

A recent study in the June 2017 issue of the journal Neurosurgery entitled “Factors influencing the reliability of the Glasgow coma scale: a systematic review” studies the overall reliability of the Glasgow coma scale in a variety of settings clinical

The review identifies multiple limitations that include the knowledge of the evaluator. The level of education and training of the medical professional can alter the score.

Glasgow pediatric coma scale

Another significant limitation of the Glasgow coma scale, as originally developed, is that it does not accurately measure traumatic brain injury in children under 5 years of age. The so-called ‘Glasgow Pediatric Coma Scale (PGCS)’ includes modifications for this patient population.

Similar to the adult version, the sum of the ocular response, the motor response and the verbal response is equal to the pediatric Glasgow coma scale. The highest score is 15 (fully awake and conscious) and the lowest is 3 (deep coma or brain death).

Eye response:

  • Do not open your eyes (+1).
  • Open your eyes in response to pressure (+2).
  • Open your eyes in response to speech (+3).
  • Open your eyes spontaneously (+4).

Verbal response:

  • Without verbal response (+1).
  • Inconsolable, agitated (+2).
  • Inconsistently inconsolable, moaning (+3).
  • Cries but inappropriate, consoleable interactions (+4).
  • Smile, be oriented to sounds, follow objects, interact (+5).

Motor response:

  • No motor response (+1).
  • Extension to pain (decerebrate response) (+2).
  • Abnormal pain flexion in a baby (decorticated response) (+3).
  • The baby withdraws from the pain (+4).
  • The baby withdraws from touch (+5).
  • The baby moves spontaneously or intentionally (+6).

The Glasgow coma scale and the pediatric Glasgow coma scale can be confusing at times, but understanding the basics is the first step in mastering the scale.

Talking to advanced practice nurses and the rest of the medical team to determine the proper Glasgow coma scale for a patient can help direct the patient’s attention.


The inter-rater reliability of the Glasgow coma scale is p = 0.86. Some investigations have subdivided inter-rater reliability for each subscale. For the sight score, inter-rater reliability is p = 0.76, the verbal score is p = 0.67, and the motor score is p = 0.81.

Research for test-retest reliability is not recent and should be updated; however, the best available evidence is k = 0.66-0.77.

Based on a recent systematic review, the total score is typically less reliable than the individual components with a total Kappa value of 77% compared to the eye, motor, and verbal scores that had Kappa values ​​of 89%, 94%, and 88%. % respectively.


The validity of the Glasgow coma scale is affected because many hospitals administer the test while patients have been sedated, often underestimating patient scores.

It is also difficult to obtain accurate scores when patients are intubated. Recent research has refuted that intubation causes significantly different survival rates with the verbal score of r = 0.90 and the total score of r = 0.97.

The motor score is consistently the most predictive component of the Glasgow coma scale.


Given the best current available evidence, the Glasgow coma scale has a low sensitivity (56.1%) and a high specificity (82.2%). Therefore, there are very few false positives that predict a low survival rate in healthy individuals.

It is argued that the Glasgow coma scale does not accurately score patients who are intubated and does not evaluate brain stem reflexes, which may explain their low predictive capacity.

A Glasgow comma scale administered at 24 hours after injury has a odds ratio of 0.4 to predict in-hospital mortality. When administered at 72 hours after the injury, the odds ratio improves to 0.59 to predict in-hospital mortality.

Evidence suggests that the Glasgow coma scale has 71% accuracy in predicting functional independence after injury.

The Glasgow coma scale is also modestly correlated with the Disability Rating Scale (-0.28) and the Cognitive component of the Functional Independence Measure (0.37).