Platelet transfusion thresholds for vascular access

We read with interest the safe vascular access guidelines from the Association of Anaesthetists [1], which provide welcome pragmatic guidance for clinicians inserting vascular access devices in patients with coagulopathy or thrombocytopaenia. Many clinicians will recognise a lack of robust clinical evidence to underpin the strength of any recommendations. Although the working party noted the recommendations and thresholds for transfusion provided in the British Society of Haematology guidelines [2], at the time of formulating these guidelines, the panel (including one author on this letter) noted the paucity of high-quality data. Other recent international platelet guidelines [3] also recognise the challenges of providing guidance for the use of prophylactic platelet transfusions in critically ill patients. The guidelines state that, compared with guidance from the British Society of Haematology, “lower platelet counts are acceptable before transfusion should be necessary”, but there is a pressing need to generate high-quality data. Platelets are immune cells and transfusions come with risks, but they may also have an important role in reducing bleeding-associated complications [4]. The Thresholds for Platelets (T4P) trial (ISRCTN79371664) is currently investigating the optimal risk–benefit transfusion thresholds for low-bleeding-risk invasive procedures. The trial aims to recruit 2550 patients who are critically ill across 80 ICUs in the UK and Australia and has enrolled over 900 patients to date. Included participants are allocated randomly across five equally spaced platelet transfusion thresholds (< 10 to < 50 × 109.l-1). By implying that lower platelet counts are safe, the guideline recommendations may inadvertently weaken equipoise in precisely the area that T4P seeks to clarify. The presence of such divergent thresholds among different international societies highlights the need for ongoing research (Table 1). We agree with the working party that the incidence of clinically important bleeding is low, but it is important to acknowledge that this risk will vary among heterogeneous patient groups, especially those being cared for in the ICU. We are also unclear on the statement that individuals “may choose to use additional tests, such as thromboelastography and platelet mapping”. Although their use is recommended in patients undergoing major cardiac surgery or liver surgery, and in those experiencing traumatic haemorrhage [5], we are unaware of any evidence on their use to guide management of coagulopathy in invasive procedures. A brief clarification of these points would help the clinical readership of Anaesthesia interpret this section with further scrutiny and maintain research engagement in this important area. Appendix S1. Thresholds for Platelets trial investigators. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.