Factor V Leiden mutation is a risk factor for CVT and may be the most common inherited coagulation defect associated with this condition.

Summary The pediatric hemostatic balance, which is different from that in adults, is an evolving process as the hemostatic system changes and matures throughout the time from fetal to adult life, particularly in the first months of life. The concept of developmental hemostasis was confirmed by several studies evaluating different patients’ population in various technical conditions. All these studies demonstrated that, at birth, the plasma levels of most coagulation factors were around half that found in adults, the preterm newborns having lower levels than full‐term newborns. Adult values were usually reached between a few months of age and up to above 16 years for specific parameters. If the global trends are consistent across the studies, differences in absolute values could be demonstrated that are likely due to differences in the reagents and/or the instruments used. Accordingly, it is recommended by the Perinatal and Pediatric Haemostasis Subcommittee of the Scientific and Standardization Committee of the ISTH for each laboratory to define the age‐dependent reference ranges using its own technical condition. The understanding of that concept of developmental hemostasis, which is now universally accepted, is critical to ensure optimal prevention, diagnosis, and treatment of thrombotic and hemorrhagic diseases in children. Actually, developmental hemostasis could affect the interaction between anticoagulant drugs and the coagulation system and so explain in part the discrepancy between anticoagulation in adults and in children. Finally, developmental hemostasis could probably provide a protective mechanism for neonates and children, contributing to the decreased risk of thrombosis and/or bleeding in these age‐groups.

Background Recent literature reports a strong thrombotic tendency in patients hospitalized for a Covid‐19 infection. This characteristic is quite unusual and seems specific to Covid‐19 infections, especially in their severe form. Viral infections can trigger acquired thrombophilia which can then lead to thrombotic complications. We investigate for the presence of acquired thrombophilia, which could participate in this phenomenon and report their prevalence. We also wonder if these thrombophilias participate in the bad prognosis of severe Covid‐19 infections. Methods and Results In 89 consecutive patients hospitalized for Covid‐19 infection we found a 20% prevalence of protein S deficiency and a very high ie.: 72% prevalence of antiphospholipid antibodies: mainly lupus anticoagulant. The presence of PS deficiency or antiphospholipid antibodies was not linked with a prolonged aPTT nor with D‐dimer, fibrinogen or C‐reactive protein concentrations. These coagulation abnormalities are also not linked with thrombotic clinical events occurring during hospitalization nor with mortality. Conclusions We assess a high prevalence of positive tests detecting thrombophilia in Covid‐19 infections. However, in our series, these acquired thrombophilias are not correlated with the severity of the disease nor with the occurrence of thrombotic events. Albeit the strong thrombotic tendency in Covid‐19 infections, the presence of frequent acquired thrombophilia may be part of the inflammation storm of Covid‐19 disease and should not systematically modify our strategy on prophylactic anticoagulant treatment which is already revised upwards in this pathology.

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Understanding of developmental haemostasis is critical to ensure optimal prevention, diagnosis, and treatment of haemorrhagic and thrombotic diseases in children. As coagulation test results are known to be dependent on the reagents/analysers used, it is recommended for each laboratory to define the age-dependent reference ranges by using its own technical condition. That study was carried out in seven centers to establish age-specific reference ranges using the same reagents and analyser. Plasma samples were obtained from 1437 paediatric patients from the following age groups: 15 days-4 weeks (n=36), 1-5 months (n=320), 6-12 months (n=176), 1-5 years (n=507), 6-10 years (n=132) and 11-17 years (n=262). Indication of coagulation testing was pre-operative screening for non-acute diseases in most cases. PT values were similar in the different age groups to those in adults, whereas longer aPTTs were demonstrated in the younger children. Plasma levels of all clotting factors, except for FV, were significantly decreased (p<0.0001) in the youngest children, adult values being usually reached before the end of the first year. The same applied to antithrombin, protein C/S, and plasminogen. In contrast, FVIII and VWF levels were elevated in the youngest children and returned to adult values within six months. The same applied to D-dimer levels, which were found elevated, particularly until six months of life, until puberty. These data suggest that most coagulation test results are highly dependent on age, mainly during the first year of life, and that age-specific reference ranges must be used to ensure proper evaluation of coagulation in children.

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Individualized anticoagulation management and improvement of the safety and effectiveness of oral anticoagulant have always been the focus of clinicians' attention. D‐dimer, a sensitive marker of thrombosis and coagulation activation, is not only traditionally used in the diagnosis of venous thromboembolism, acute aortic dissection, and disseminated intravascular coagulation but can also be used as a helpful marker in the management of oral anticoagulant, including evaluating the anticoagulation quality, predicting clinical outcomes, and determining the optimal duration and intensity of anticoagulation.

Summary Introduction A maximum delay between blood collection and coagulation testing of 4 hours is recommended by most guidelines. As information on optimal storage times is limited, we investigated the potential effect of different storage times of unspun tubes, that is, ≤2, 4, 6, and 8 hours, on routine coagulation test results. Methods Four evacuated polymer tubes containing 0.109 mol/L tri‐Na citrate were drawn from 144 patients, including 39 patients on vitamin K‐antagonists. Except for storage time, all tubes underwent the same preanalytical process. Prothrombin time (PT)/international normalized ratio (INR), activated partial thromboplastin time (aPTT), fibrinogen, factor V (FV), FVIII, and D‐dimer were evaluated in two centers using the same technical conditions. Results Analytical comparison of aPTT, fibrinogen, FV, and FVIII results evaluated after prolonged storage times vs a <2‐hours storage demonstrated significant difference, whereas PT/INR and D‐dimer remained unchanged up to 8 hours. Mean bias between test results obtained after prolonged storage times remained below the desirable values for all studied parameters except for FVIII evaluated after 6‐ and 8‐hours storages, but only in patients with FVIII above 100 IU/dL. Even though the corresponding bias of −5.2% and −8.5%, respectively, remained within the GEHT recommended limits of variation, its evaluation after an 8‐hours storage could lead to significant underestimation of FVIII. Conclusion These results suggest that, in the studied technical conditions, PT/INR, aPTT, fibrinogen, FV, and D‐dimer can be reliably evaluated in tubes stored unspun at room temperature for up to 8 hours after blood collection. That optimal delay should be of 6 hours for FVIII.