In the United Kingdom (UK), around 250,000 platelet transfusions are given out every year. Platelet transfusions are given when the number of platelets in the blood (the platelet count) falls below a certain level (the transfusion threshold). Platelet transfusions are commonly given in critical care units as patients in critical care often have fewer platelets in their blood than healthy people. In critical care units, platelet transfusions are mainly given to try and prevent bleeding, for example during a procedure.

However, platelet transfusions also have risks, such as an allergic reaction, and may not work as well in critical care unit patients. We do not know to what level the platelet count should fall (the best transfusion threshold) before the benefits of giving platelet transfusions outweigh the risks. As a result, a wide range of transfusion thresholds are currently used in critical care units to decide when platelet transfusions should be given.


We intend to carry out a large clinical trial to find out the best transfusion threshold below which platelet transfusions should be given to patients who need an invasive procedure in critical care. The study will include 2,550 patients from around 66 UK NHS critical care units. Patients will be randomly allocated (by chance) to one of five platelet transfusion thresholds. If their platelet count drops below their allocated threshold, they will be given a platelet transfusion before their procedure. We will follow up all patients, after 90 days and one year, by linking study data with routinely collected national records. We will work out the best transfusion threshold by comparing the number of patients alive in each group at 90 days. 

Results from this study will have a large and immediate impact on clinical practice in critical care, as well as wider benefits throughout the NHS.

Key information

Chief investigator(s)

Professor Peter Watkinson, University of Oxford


University of Oxford


National Institute for Health and Care Research (NIHR) – Health Technology Assessment (HTA) Programme 

(Project Number: NIHR131822)

Trial registration(s)

ISRCTN Registry: ISRCTN79371664

NIHR Central Portfolio Management System: 53274

Contact information

Trial Manager: Hayley Noble


Phone: 020 7269 9284