What is known?
Patients with severe thrombocytopenia (very low platelet count) due to a hypoproliferative bone marrow (markedly reduced platelet production) receive prophylactic (given to prevent bleeding) platelet transfusions. This usually occurs when the platelet count drops below a certain threshold (the current standard is a platelet count of 10 x 109/l). Platelet transfusions are known to be associated with risks. Mild to moderate reactions to platelet transfusions include rigors (severe shivering accompanied by a feeling of coldness), fever, and urticaria (hives). These reactions are not life-threatening but can be extremely distressing for the patient. Rarer, but more serious side effects include: transfusion-transmitted infections (bacterial and viral infections) and transfusion-related acute lung injury (TRALI).
What did this paper set out to examine?
This is a secondary analysis of the PLADO Study (Slichter et al, 2010). The authors set out to show whether the characteristics of the patient receiving the platelet transfusion (patient’s age, sex, type of treatment, number of previous platelet transfusions) or of the platelet component itself (whether the platelets were ABO matched with the patient, how the platelet component had been produced, number of platelets within the transfusion, number of days the platelets had been stored for) affected the frequency of transfusion-related adverse events (TRAEs) after platelet transfusions. In this study TRAEs were any event that occurred within 4 hours of the platelet transfusion irrespective of whether medical staff at the time thought the event was related to the transfusion. TRAEs consisted of at least one of the following: allergic or hypersensitivity reaction; slow or fast heart rate; high or low blood pressure; shortness of breath; low oxygen levels; wheezing; cough; rigors or chills, fever, infection, or haemolysis (breakdown of red blood cells). The severity of TRAEs were graded. Multivariable analyses were carried out that compared any TRAE versus none, any TRAE of Grade 2 or above versus none, and any TRAE of Grade 3 or above versus none. As well as analyses of specific TRAEs that occurred in at least 50 (1%) of transfusions in the analysis.
What did they show?
Fever (6.6%) and allergic reactions (1.9%) were the most common TRAEs. A multipredictor logistic regression model for any TRAE versus no TRAE, which adjusted for all other variables in the model and for within-person correlation. This study found that a high number of platelets within the component increased the risk of a TRAE (odds ratio for high platelet number vs. intermediate platelet number, 1.50; 95% confidence interval, 1.10-2.05). This effect was no longer seen when only grade 2 or above TRAEs were considered, however this may be due to the small number of episodes observed. Compared to a patient’s first platelet transfusion, participants who had more than five platelet transfusions were less likely to have a TRAE reported during subsequent transfusions. This was primarily due to a lower risk of allergic or hypersensitivity reactions.
What are the implications for practice and for future work?
The primary publication of the PLADO study showed that a large number of platelets within a transfusion does not decrease the risk of WHO grade 2 or above bleeding, and does not reduce the number of transfusion episodes compared to an intermediate number of platelets within a component. This study now shows that platelet components that contain a large number of platelets may put patients at a higher risk of developing a TRAE. This study provides an additional reason why platelet components that contain a high number of platelets should not be used routinely.