The Planet-2 trial that I posted about when it first came out showed no benefit among preterm infants, <34 weeks gestation when they received platelet transfusions at a threshold of 50,00 compared to waiting until they dropped to 25,000.
I didn’t find the lack of benefit overall in the high threshold group particularly surprising. What was unexpected was that using the lower threshold actually had benefits in terms of a substantial increase in survival without subsequent serious bleeding, 19% vs 26%. The benefits seemed to be both in death, about a 5% absolute reduction, and serious bleeding, about a 3% absolute reduction. The lower threshold babies also had less BPD, a 9% absolute reduction among survivors.
A newly published secondary analysis of the trial asks the question whether the benefit of a lower transfusion threshold applies to all the risk subgroups, or just to lower risk patients. In other words if a baby is at very high risk of bleeding, then perhaps we should continue to consider a higher threshold. (Fustolo-Gunnink SF, et al. Preterm neonates benefit from low prophylactic platelet transfusion threshold despite varying risk of bleeding or death. Blood. 2019).
To answer this question you could look at specific high risk groups (such as babies who are thombocytopenic in the first 3 days of life); that was already published as a supplememtary analysis with the original paper, and in fact the relative, and absolute, benefit of a lower threshold on the primary outcome was greatest among babies randomized before 72 hours of life, 11% vs 25%.
An alternative method is to determine risk categories from data collected during this trial, which is what this group have done, creating a logistic regression model of risk of the primary outcome (survival without further serious bleeding) and then dividing the infants into quartiles of risk based on the model. They then showed that all quartiles of risk had a benefit from a lower transfusion threshold, and in fact the highest absolute benefit was in the quartile with the highest risk.
This is further evidence that we can apply the lower threshold to all of our preterm babies with throbocytopenia.