Discovery of four COVID-19 risk groups helps guide treatment

Two medics walking next to a hospital bed

People who are admitted to hospital with COVID-19 can be divided into four distinct groups, according to data from the world’s largest study of patients with the disease.

Researchers identified the groups using clinical information and tests carried out upon arrival at hospital to predict the patients’ risk of death – ranging from low to very high.

A COVID-19 risk identification tool – the most accurate to date – has been designed using the groupings to help clinical staff choose the best course of treatment for patients admitted to hospital.

About the tool

The tool was built by the International Severe Acute Respiratory and Emerging Infection Consortium (ISARIC) Coronavirus Clinical Characterisation Consortium (ISARIC 4C) involving researchers from universities of Edinburgh, Glasgow, Liverpool and Imperial College London using data from some 35,000 patients admitted to hospital between February and May 2020 who met the criteria for one of the four groups.

The tool was then tested and confirmed to be accurate using data from a further 22,000 patients hospitalised from the end of May to the end of June 2020.

The research was funded by UK Research and Innovation (UKRI) and by the Department of Health and Social Care through the National Institute for Health Research as part of the UK government’s COVID-19 rapid research response.

Some of the data used to identify which group a person falls into – and, therefore, their risk of dying – included:

  • age
  • sex
  • the number of pre-existing conditions
  • respiratory rate on admission
  • results of two blood tests.


One in every hundred patients in the low-risk group was found to be at risk of dying. It was 10 in 100 patients in the intermediate-risk group, 31 in 100 in the high-risk group and 62 in 100 in the very high-risk group.

The categorisations make new treatment pathways possible, researchers say.

For example, it might be more appropriate for those who fall into the low-risk subgroup to be treated at home. In contrast, people in the high or very high-risk groups could benefit from more aggressive treatment, such as the use of antivirals and early admission to critical care.

Existing tools

Until now there has not been an accurate risk tool for COVID-19 patients. Existing tools for pneumonia or sepsis do not offer accurate predictions due to the differences between diseases.

Previous attempts to build a risk prediction tool for COVID-19 have had limited success due to small sample sizes and lack of formal validation. One limitation of this new tool, however, is that it can only be used on hospital patients and not within the community.

The work is the latest result from ISARIC – a global network of clinicians and scientists who have been preparing to prevent disease and death from severe outbreaks since 2012 in readiness for a pandemic such as this. It involved 260 hospitals across England, Wales and Scotland. The ISARIC 4C study includes two thirds of all people admitted to hospital with COVID-19.

The research findings are published in the BMJ: Risk stratification of patients admitted to hospital with COVID-19 using the ISARIC WHO Clinical Characterisation Protocol: development and validation of the 4C Mortality Score.

Professor Fiona Watt, Executive Chair of the Medical Research Council, part of UKRI, said:

These results highlight the benefits of being prepared in advance of the emergence of new pandemics such as COVID-19. ISARIC is a global network of clinicians and scientists that was set up in 2012 in readiness for a pandemic such as COVID-19, and its value is evident from the findings described today.

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