A systematic review identified three RCTs that compared different platelet transfusion thresholds in patients with haematological malignancies (20). Two compared a threshold of 20 x 109/L vs. 10 x 109/L, whereas the third compared a threshold of 30 x 109/L vs. 10 x 109/L. There was no evidence of a difference in the number of participants with a clinically significant bleeding episode between the 10 x 109/L threshold and higher threshold groups (three studies; 499 participants; risk ratio (RR) 1.35, 95% confidence interval (CI) 0.95 to 1.90; low-quality evidence). However, this meta-analysis may not be sufficiently powered to detect a 50% increase in bleeding risk. There has been a suggestion that platelet transfusion thresholds should be lowered below 10 x 109/L, but current platelet count measurement is not accurate enough to support this change (21). No randomised studies in adult patients have assessed the use of other transfusion thresholds, such as platelet mass, absolute immature platelet number or immature platelet fraction. Neonates admitted to the neonatal intensive care unit (NICU) frequently become thrombocytopenic and intracranial haemorrhage (ICH) is a major concern. Guidelines directing neonatal platelet transfusion practice vary considerably, and are generally consensus rather than evidence-based. There has only been one RCT in preterm neonates comparing different platelet count thresholds this found no difference in the incidence of ICH between a liberal platelet transfusion regimen (transfusion when platelet count < 150x109/L) versus a more restrictive regimen (platelet count < 50x109/L or clinical concern about bleeding) (22). One small pilot RCT has compared a platelet mass versus platelet count regimen and found no difference in the number of bleeding events (23). There are two ongoing trials assessing different platelet transfusion thresholds (24, 25).
Therapeutic platelet transfusions
There is little evidence for the effectiveness of platelet transfusions or the optimal dose when a person with thrombocytopenia is actively bleeding. Current recommendations are based on consensus guidelines from around the world and are dealt with in [ISBT section on major haemorrhage].