CoaguLopathy in COVID-NineTeen (The CLOT Study) 


UHB, UoB, UCL, UCLH, The Turing, Cambridge, LSHTM 

Lay Summary: 

In March 2020 the World Health Organisation (WHO) declared the disease, COVID-19, caused by the virus SARS-CoV-2, a pandemic. Although most people infected with the virus have no, or very mild symptoms, in 20% of those infected, the symptoms are bad enough to require medical attention and admission to hospital. 


Doctors and nurses caring for COVID-19 patients in hospital noticed that patients were suffering with more symptoms caused by blood clots in the veins and arteries of the lungs and legs than would be expected.  These blood clots can have serious effects.  They can make the lungs work less effectively which is a serious concern, especially if COVID has already compromised lung function.    There are drugs which can prevent blood clots from forming (called anticoagulants) but these do not seem as effective in patients with COVID-19.   


We know little about why, how, and when these clots form or which patients are most at risk of developing them.   


At present it is even difficult to say how many patients admitted to the hospital developed clots.  We have to analyse data from thousands of patients to understand the disease better. 


By looking at the very large data pool of DECOVID,  this project will try to answer three important questions: 

• How often do clots form in patients whose symptoms require hospital admission? 

• Why do the clots form more easily in these patients? 

What kind of patients are most likely to develop clots? 

• Do any of currently used methods of clot prevention work? 

Answering these questions will help us design effective strategies to deal with clotting problems in patients with COVID-19. 


The results will be shared in open access journals, so that as many people as possible can benefit from what we learn.  All analytical code (the computer code we use to analyse the data) will also be made available any researchers, to ensure that our research follows “FAIR” principles (Findable, Accessible, Interoperable and Reusable). 

Scientific Summary: 

Estimates for the proportion of patients admitted to hospital for COVID-19 who have laboratory evidence of prothrombotic coagulopathy range from 20 - 55%. Thrombotic complications are associated with high mortality and morbidity in patients with a COVID-19 infection. Age, severity of illness, and pre-existing conditions appear to be risk factors, as does the severity of COVID-19 on presentation. However, presentation is heterogeneous and currently we do not understand which patients are at greatest risk. 


Existing studies assessing coagulopathy so far have been small and have presented insufficient detail, limiting their ability to inform the choice of clinical treatment strategies. 

Comparing the prevalence, patient factors and treatments across participating DECOVID trusts would provide significant insight. 


Primary objective: 

To assess the incidence, severity, risk factors and clinical trajectory of clinically significant venous thromboembolism (VTE) in hospital patients with COVID-19. 


Secondary objectives: 

We will also assess: 

• Whether we can predict VTE. 

• If any management strategies may prevent VTE. 

• What the consequences of VTE for COVID patients are. 

We will also consider two other coagulopathic events: arterial thromboembolism (ATE), and 



Detailed study questions: 

1. Do the routinely collected outcomes captured in the DECOVID dataset accurately reflect 

the incidence of VTE? 

2. What is the incidence of VTE in hospital patients with COVID-19? 

3. What is the time of manifestation of VTE during hospital admission in patients with 


4. What are the risk factors of VTE in hospital patients with COVID-19? 

5. Is there an association between severity of COVID-19 (SARS-CoV-2 infection) at hospital 

admission and VTE? 

6. Are temporal changes in COVID-19 severity and physiological, biochemical, and haematological parameters associated with incidence of VTE? 

7. What is the impact of developing VTE on the clinical course of COVID-19, defined as need 

for organ support, admission to ICU, length of hospital stay (overall, and separately by the 

general ward and ICU), and mortality? 

8. Are different management strategies (pharmacological prophylaxis, anticoagulation, mechanical prophylaxis, or combination) associated with different risk of development of VTE in patients with COVID-19? 

We will also examine these questions for ATE and bleeding.