Using platelets in haematology: new studies
A significant proportion(about 60%) of platelet (plt) concentrates are administered to patients with haematological malignancies, and more ‘aggressive’ treatment regimens are increasingly being used, with higher risks of toxicity. Around 70% of plts are used to prevent bleeding (prophylaxis). Therapeutic plt transfusions (Txs) are accepted as an effective treatment for thrombocytopenic patients who are bleeding, but aspects of prophylactic plt Tx therapy in patients with bone marrow failure remain controversial. Recent meta-analyses have re-evaluated the evidence for the optimal dose and thresholds for prophylactic plt Txs. It seems clear that there is no significant difference in the number of patients who bleed when they receive different doses of plt components. However, the summary statistics for trials comparing ‘liberal’ and ‘restrictive’ use of plts showed more heterogeneity. It is unclear whether the bleeding rate is the same when comparing a plt count of 10x109/L vs. higher thresholds. The recording of bleeding in these trials showed considerable variability and many of the bleeding events in these studies were relatively minor. Two recently completed randomised-controlled trials have addressed the question of whether a prophylactic plt Tx strategy is appropriate and safe in all subgroups of patients with haematological malignancies, but the results of these studies are awaited. One of the main reasons for administering plt Txs in patients with haematological malignancies is to prevent intracranial bleeding. An ongoing national case-control study aims identify the frequency of this event and associated risk-factors. Currently, 50 patients with ICH have been reported. Plt Txs are associated with well described risks, and there is interest in the role of pathogen-reduced platelet (p-Rx) components. A recent review has shown that p-Rx components did not lead to an increased risk of bleeding (RR 1·1495%CI 0·93 to 1·38; P = 0·2).However, they did show a significant reduction in the plt count increment and corrected count increment (CCI) at 1hr and 24hrs post Tx (24 hr CCI RR −3·09 95% CI −3·71 to −2·46; P =< 0·00001), as well as a significant increase in the number of plt Txs per day, and an increase in the number of patients with plt refractoriness (RR 2·75 95% CI 1·84 to 4·07; P =< 0·00001). Other areas for future research include the prophylactic use of plts before procedures such as central line insertion, lumbar puncture and epidural anaesthesia, and in patients with sepsis. Some recent studies have suggested that it is safe to perform central line insertion at plt counts above 20 to 25x109/L. Given the uncertain relationship between degree of thrombocytopenia and clinical bleeding, a better understanding of all haemostatic changes in patients with haematological malignancies may inform new strategies to reduce bleeding risk.