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

Designed in 1974, it is a tool that can communicate patients’ level of awareness of 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 damage (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.

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

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

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


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

The population is expected to use the Glasgow coma scale.

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

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 various settings, such as prehospital, arrival at the emergency department, and hours after admission, allowing 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 using 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 evaluating older and preverbal children when studying closed traumas.

When to use it?

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

The Glasgow coma scale should be performed at 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).
  • Note: 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).
  • Introduced: Correctly indicates the name, place, and date (+5).

Motor response:

  • Not verifiable: Paralyzed or another 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 and presents a predominantly strange characteristic (+3).
  • Normal flexion: Folds the arm at the elbow quickly but does not give an essentially 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 scale above 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 the three main areas.

Once a number has been determined, add these to create the sum that is the patient’s Glasgow score. Once a score has been identified, it is essential 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 and 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. In contrast, a patient with pronounced ocular swelling would have a visual reaction of 1c that would identify the eyes as closed and unable to open due to swelling.


While the Glasgow coma scale is an excellent diagnostic tool, multiple limitations 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 (natural and academic).
  • 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 in clinical

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

Glasgow pediatric coma scale

Another significant limitation of the Glasgow coma scale, as initially developed, is that it does not accurately measure traumatic brain injury in children under five 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, consolable interactions (+4).
  • Smile, be oriented to sounds, follow objects, and 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 starts 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 challenging 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 currently available evidence, the Glasgow coma scale has a low sensitivity (56.1%) and a high specificity (82.2%). Therefore, significantly few false positives 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 24 hours after the injury has an odds ratio of 0.4 to predict in-hospital mortality. When administered 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 an 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).