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The Platelets for Neonatal Thrombocytopenia (PlaNeT-2) trial reported an unexpected overall benefit of a prophylactic platelet transfusion threshold of 25 × 109/L compared with 50 × 109/L for major bleeding and/or mortality in preterm neonates (7% absolute-risk reduction). However, some neonates in the trial may have experienced little benefit or even harm from the 25 × 109/L threshold. We wanted to assess this heterogeneity of treatment effect in the PlaNet-2 trial, to investigate whether all preterm neonates benefit from the low threshold. We developed a multivariate logistic regression model in the PlaNet-2 data to predict baseline risk of major bleeding and/or mortality for all 653 neonates. We then ranked the neonates based on their predicted baseline risk and categorized them into 4 risk quartiles. Within these quartiles, we assessed absolute-risk difference between the 50 × 109/L- and 25 × 109/L-threshold groups. A total of 146 neonates died or developed major bleeding. The internally validated C-statistic of the model was 0.63 (95% confidence interval, 0.58-0.68). The 25 × 109/L threshold was associated with absolute-risk reduction in all risk groups, varying from 4.9% in the lowest risk group to 12.3% in the highest risk group. These results suggest that a 25 × 109/L prophylactic platelet count threshold can be adopted in all preterm neonates, irrespective of predicted baseline outcome risk. Future studies are needed to improve the predictive accuracy of the baseline risk model. This trial was registered at www.isrctn.com as #ISRCTN87736839.

Introduction Limited evidence supports the widely used practice of administering platelet transfusions to prevent major bleeding in preterm thrombocytopenic neonates. Only 1 randomized controlled trial addressed this issue, but used thresholds higher than those currently used in clinical practice. In order to assess the impact of platelet transfusions on bleeding risk, the primary objective of this study was to develop a prediction model for bleeding. Platelet transfusion was included as variable in this model. In these secondary analyses, we further explored the impact of platelet transfusions on bleeding risk. Materials and methods In this multicenter cohort study, neonates with a gestational age (GA) 20x109/L only allowed in case of GA Results A total of 640 neonates were included with a median gestational age of 28 weeks. 70 neonates developed a major bleed. IUGR, postnatal age, platelet count and mechanical ventilation were independent predictors of bleeding. The model allowed calculation of two bleeding risks for individual neonates: one in case of platelet transfusion and one in case of no platelet transfusion. 1361 platelet transfusions were administered to 449 of 640 (70%) neonates, of which 87 were hyperconcentrates. The hazard ratio for transfusion in the original model was 1.0, indicating no predictive power. Sensitivity analysis 1: 704 (52%) transfusions were given according to protocol. When selecting these transfusions, the hazard ratio for transfusion changed from 1.0 to 0.5, but the p-value remained > 0.05.Sensitivity analysis 2: 764 (56%) of transfusions resulted in a count >50x109/L within 24 hours. When selecting these transfusions, the hazard ratio for transfusion changed from 1.0 to 0.25, but the p-value remained >0.05. 115 (8%) transfusions did not have a follow up platelet count within 24 hours. Sensitivity analysis 3: of the non-hyperconcentrated platelet transfusions, 517 of 1274 (41%) transfusions were ≥ 11 ml/kg. When selecting these transfusions, the hazard ratio for transfusion changed from 1.0 to 0.1, with a p-value of 0.05. Conclusion With this tool, absolute risk of bleeding in individual preterm thrombocytopenic neonates can be calculated. Additionally, risk of bleeding can be assessed for 2 scenarios: with and without platelet transfusion. This can help clinicians in deciding whether or not to transfuse a patient. In the primary model, platelet transfusion was not a predictor for bleeding risk. However, the findings of the sensitivity analyses suggest that transfusions with a dose > 11ml/kg may have a more profound effect on bleeding risk. Disclosures No relevant conflicts of interest to declare.