Use of an Antifibrinolytic Agent and Vitamin K As Alternative to Platelet Transfusions in Autologous Hematopoietic Cell Transplantation

Vitamin K is involved in blood clotting, and lack of this nutrient results in a hypocoagulable state, associated with a high risk of bleeding events. Deficiency is rare among adults, because vitamin K is widely available in foods. However, the placenta transmits vitamin K relatively poorly, leading to a general deficiency in full-term neonates, who are also particularly vulnerable to the effects of low vitamin K levels because of their immature clotting systems. Deficiency can lead to intracranial haemorrhage following birth trauma, or classic vitamin K deficiency bleeding. It is important to maintain adequate vitamin K status throughout pregnancy in order to avoid added risk to the neonate at birth and in the first few weeks of life. Supplementation of newborns by intramuscular injection should be universal.

Aim: Although 40-65% of myelodysplastic syndromes (MDS) patients are thrombocytopenic and require platelet transfusions, there is limited literature on the risk factors predictive of bleeding and the burden of immune mediated platelet refractoriness (PLT-R). Objectives: To evaluate the prevalence of thrombocytopenia, incidence of bleeding events, platelet transfusion dependency (PLT-TD) and immune-mediated platelet refractoriness (PLT-R) in MDS patients. Methods: A retrospective analysis of 754 MDS patients enrolled in the South Australian MDS (SA-MDS) registry was performed. Platelet counts <100, <50 and <20 (x109/L) were used to define mild, moderate and severe thrombocytopenia respectively. The severity of bleeding events was classified according to the International Society of Thrombosis and Haemostasis (ISTH) classification. PLT-TD was defined as transfusion of at least one unit of platelets each month for four consecutive months. All other patients were classified as transfusion independent (PLT-TI). Immune mediated PLT-R was defined if a patient had HLA-class I or HPA antibodies, poor platelet increments and required HLA-matched platelets. Medication history with regards to anticoagulation and/or antiplatelet therapy was also collected. Results: At diagnosis, 332 (45%) patients had thrombocytopenia and 106 (14%) patients had moderate to severe thrombocytopenia. During the study period, 249 bleeding events were recorded in 162 (21%) patients with a cumulative incidence of 33% (Fig 1A). Of the 249 bleeding events, 85 (34%) were major and 164 (66%) were clinically relevant minor bleeding. Notably, 16, 90 and 5 bleeding events were intracranial, gastrointestinal, intraocular respectively. While 41% (96/235) bleeding events occurred in the setting of moderate to severe thrombocytopenia, 21% and 38% (Fig 1B) of bleeding events occurred at platelet counts of >50-100 and >100x109/L respectively. Twenty-eight percent (69/249) bleeding events were associated with concomitant anticoagulation and/or antiplatelet therapy and importantly, platelets counts were >50x109/L and >100 x109/L in 57 (83%) and 46 (67%) at the time of bleeding events, respectively. During the disease course, 393 (52%) patients required at least one unit of platelet transfusion. 106 (14%) patients were PLT-TD and had significantly poor overall survival (OS) compared to PLT-TI (26 vs 42 months, p<0.0001). In total, 30/393 (7%) required HLA-matched platelet transfusions. 20/30 (66%) of PLT-R patients were female receiving disease modifying therapy (DMT). This was substantiated by cox regression analysis, demonstrating that females (HR=5.32, p=0.0006), older age (HR=0.97, p=0.028) and haemoglobin (Hb) at diagnosis (HR=1.03, p=0.009) were independent risk factors for PLT-R. Importantly, 20/76 (25%) female patients receiving platelets and DMT developed immune mediated PLT-R requiring HLA matched platelets. Conclusions: In our cohort of MDS patients, cumulative incidence of bleeding is 33% and 59% of the bleeding events occurred at platelet counts >50X109/L. For all bleeding events that occurred while on anticoagulation and/or antiplatelet therapy, 83% events occurred with platelet counts >50 x 109/L. Therefore, guidelines for anticoagulation and/or antiplatelet therapy are required for MDS patients. We also showed that development of PLT-TD is associated with poor OS. Importantly, 1 in 4 female MDS patients receiving platelets and DMT required HLA-matched platelets. Platelet transfusions practices should be optimised for these high-risk groups. Disclosures No relevant conflicts of interest to declare.

SummaryVitamin K status was evaluated using coagulation studies and/ or vitamin IQ assays in a total of 53 normal fetuses and 47 neonates. Second trimester fetal blood samples were obtained for prenatal diagnosis under ultrasound guidance. Endogenous vitamin K1 concentrations (determined by high performance liquid chromatography) were substantially lower than maternal levels. The mean maternal-fetal gradient was 14-fold at mid trimester and 18-fold at birth. Despite low vitamin K levels, descarboxy prothrombin, detected by a staphylocoagulase assay, was elevated in only a single fetus and a single neonate.After maternal oral supplementation with vitamin K1, cord vitamin K1 levels were boosted 30-fold at mid trimester and 60 fold at term, demonstrating placental transfer. However, these levels were substantially lower than corresponding supplemented maternal levels. Despite elevated vitamin K1 concentrations, supplemented fetuses and neonates showed no increase in total or coagulant prothrombin activity. These results suggest that the low prothrombin levels found during intrauterine life are not due to vitamin K deficiency.

SummaryPIVKA, the circulating anticoagulant protein found in vitamin K deficiency can, on kinetical grounds, be recognized as an analogue of factor X. The existence of analogues of other vitamin K-dependent clotting factors cannot be ruled out, but need not be assumed to explain the experimental results.