CompletedHeart, Stroke & BloodNIHR-supported projectPregnancy, Children & Inherited Conditions
The Threshold for Platelets (T4P) study: a prospective randomised trial to define the platelet count below which critically ill patients should receive a platelet transfusion prior to an invasive procedure
Recipient organisationNIHR University College London Hospitals Biomedical Research Centre
NIHR supportRecorded as supported by this research centre
PeriodFeb 2025 — Dec 2025
In plain English
AI plain-English summary
Every year, around 250,000 platelet transfusions are given in UK hospitals, but no one knows exactly how low a patient’s platelet count must fall before the transfusion does more good than harm. This uncertainty hits hardest in intensive care units (ICUs), where patients often have low platelet counts and frequently undergo invasive procedures. Doctors currently use a wide range of transfusion thresholds because the evidence is missing. Platelet transfusions carry real risks—allergic reactions, for instance—and may not work as well in critically ill patients as they do in others. The Threshold for Platelets (T4P) trial will settle this by randomly assigning 2,550 patients across 66 NHS ICUs to one of five transfusion thresholds. If a patient’s count drops below their assigned threshold, they receive a transfusion before their procedure. The team will then compare survival rates at 90 days to identify the safest, most effective threshold. If the trial succeeds, it will give ICU clinicians a single, evidence-based rule for when to transfuse. That could reduce unnecessary transfusions, cut risks for patients, and save the NHS money on a treatment given hundreds of thousands of times each year.
View original technical description
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 Intensive Care Units (ICU) as patients in ICU often have fewer platelets in their blood than healthy people. In ICUs, 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 ICU 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 ICUs to decide when platelet transfusions should be given. Therefore, 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 ICU. The study will include 2,550 patients from around 66 UK NHS ICUs. 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. Patient recruitment will start in mid-2022 and end in 2026. The results will have a large and immediate impact on ICU clinical practice, as well as wider benefits throughout the NHS.
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