What is the Glasgow Coma Scale Pupils Score?

The GCS Pupils Score (GCS-P) was described by Paul Brennan, Gordon Murray and Graham Teasdale in 2018 as a strategy to combine the two key indicators of the severity of traumatic brain injury into a single simple index.

The paper can be accessed and downloaded for free from here, where you can read about the development of the GCS-P in more detail. A summary of the background to its development can also be read at the end of this article (llnk to section below).

How do I calculate the GCS-P?

The GCS-P is calculated by subtracting the Pupil Reactivity Score (PRS) from the Glasgow Coma Scale (GCS) total score:

  • GCS-P = GCS - PRS

Further information on assessment of the GCS can be accessed here.

The Pupil Reactivity Score is calculated as follows.

Pupils Unreactive to Light Pupil Reactivity Score
Both Pupils 2
One Pupil 1
Neither Pupil 0

Case study

So, imagine that you are asked to assess a patient who has been ejected from the passenger seat of a car at high velocity. They make no eye, verbal or motor movements spontaneously, or in response to your spoken requests. When stimulated their eyes do not open, they make only incomprehensible sounds, and their arms abnormally flex. This can be scored as E1V2M3 using the Glasgow Coma Scale, giving a sum score of 6.

You now test their pupil reactivity to light. Neither pupil is reactive to light. This gives a Pupil Reactivity Score (PRS) of 2.

The GCS-P can then be determined as GCS-PRS, which in this case it 6-2 =4.

You can read from Table 2 in the paper that with a GCS 6 there is a 29% chance of death at 6 months. When the pupil reactivity and GCS are combined to give a GCSP, the mortality increases to 39% (Table 3).

What is the advantage of the GCS-P?

Separately, the GCS and the pupil response to light are both related to outcome. As you can see from the above example, combining the information together in the GCS-P extends the information provided about outcome to an extent comparable to more complex methods of combination of the data. This may improve decision making about patient care, and assist in stratification of patients into clinical trials. The score may also be a useful platform onto which information about other key prognostic features can be added in a simple format likely to be useful in clinical practice; you can read more about this in ‘GCS-PA charts’ (link to GCS-PA tab).


The work underpinning the GCS-P was published by the Journal of Neurosurgery in April 2018 as one of two joint papers from our group that sought to simplify the use of prognostic information in traumatic brain injury. The second paper describes a graphical presentation of the outcome probabilities in traumatic brain injury.

Assessment of a patient’s clinical condition, and how this is changing, is a cornerstone of the care of people with a head injury and many other kinds of acute brain damage. The Glasgow Coma Scale is widely used for this purpose, reflecting its utility in observing a patient’s responsiveness, or so called ‘conscious level,’ and communicating the findings clearly and consistently. Decisions about management are also influenced by perceptions of the relationship between a patient’s early condition and their likely outcome.

Estimates of prognosis using mathematical methods that combine information from multiple aspects of the patient’s condition have not found widespread uptake in clinical practice. Instead simple ‘scoring systems’ for stratifying severity appeal to clinicians in every field of medicine. These trade off a loss of detail and specificity of information with the ease and transparency of the calculation of the score.

Each of the three components of the Glasgow Coma Scale (Eyes, Verbal, Motor) contains information about prognosis and the findings can be combined in a summary total score, derived from simple addition of a notation assigned to its components. This is widely used as an index of ‘overall’ brain damage, which is the most important feature in distinguishing head injuries of differing severities and in monitoring their progress and prognosis. ‘Brain stem’ features were not incorporated into the scale, but were expected to be assessed separately. There have nevertheless been views that more complex scores, with extra features would be useful.

The GCS together with information about pupil reaction conveys most of the clinical predictive information in head injured patients. We, therefore, have investigated different ways of combining the information from these two key features into an index of prognosis, either mortality or unfavourable outcome (vegetative or severe disability), in acute head injured patients.