[Specificities of neonatal hemostasis and implications in pathologic situations]

The haemostasis of healthy newborn differs from those of normal adult but remains well balanced without bleeding or thrombosis. However, this equilibrium is unstable, and the neonate is exposed to acquired or inherited haemostasis disorders that necessitate to be early diagnosed in order to be appropriately treated. Several studies provided reference ranges for haemostatic components in the foetus, the newborn and throughout childhood. The particularities of neonatal haemostasis are therefore better defined and contribute to further understand the pathophysiology and characteristics of hemorrhagic and thrombotic disorders that occur in newborns. Some examples of the impact of age on haemostasis are: the risk of neonatal alloimmune thrombocytopenia is high in the first newborn of a woman at risk since the involved antigens are fully expressed by foetal platelets; the newborn is at risk for vitamin K deficiency with bleeding due to poor transport of vitamin K across the placenta and low levels of coagulation factors II, VII, IX, X; the diagnosis of some inherited coagulation deficiencies can be difficult in the newborn due to physiologically low levels of coagulation factors; thrombotic events are rare in the healthy neonate, despite physiologically very low levels of several coagulation inhibitors; the pharmacokinetic and effects of antithrombotic agents are influenced by the specificities of haemostasis in neonates. This review will discuss about the foetal development of haemostasis until birth, and some implications regarding the pathophysiology, the diagnosis and the treatment of bleeding disorders in the human neonate.

[Prolongation of anti vitamin K treatment for 18 months versus placebo after 6 months treatment of a first episode of ideopathic pulmonary embolism: a mutlicentre, randomised double blind trail. The PADIS-EP Trial]

BACKGROUND

After stopping a 3 to 6 months course of oral anticoagulation for a first episode of idiopathic venous thromboembolism (VTE), the risk of recurrent VTE is high (10% per year). In this setting, international guidelines recommend at least 6 months treatment. However, this recommendation is not satisfactory for the following reasons: (1) no randomized trial has compared 6 months to extended duration (2 years) anticoagulation; and (2), even though the frequency of recurrent VTE is similar after pulmonary embolism (PE) and deep vein thrombosis (DVT), the fatality rate of recurrent VTE after PE is higher than that after DVT.

METHODS

A French multicentre double blind randomized trial. The main objective is to demonstrate, after a first episode of symptomatic idiopathic PE treated for 6 months using a vitamin K antagonist, that extended anticoagulation for 18 months (INR between 2 and 3) is associated with an increased benefit / risk ratio (recurrent VTE and severe anticoagulant-related bleeding) compared to placebo. The double blind evaluation is ensured using by active warfarin and placebo, and blinded INR. The protocol was approved by the ethics board of the Brest Hospital on the 7th of March 2006. For an alpha risk of 5% and a beta risk of 20%, the estimated sample size is 374 patients.

EXPECTED RESULTS

This study has the potential to: (1) demonstrate that the benefit / risk ratio of extended anticoagulation for 18 months is higher than that observed with placebo in patients with a first episode of idiopathic PE initially treated for 6 months, during and after the treatment period; and (2) to validate or invalidate the contribution of isotope lung scans, lower limb Doppler ultrasound and D-Dimer at 6 months of treatment as predictors of recurrent VTE (medico-economic analysis included).

Treatment of inherited protein C deficiency by replacement therapy with the French purified plasma-derived protein C concentrate (PROTEXEL®)

BACKGROUND/OBJECTIVES

A multicentre retrospective study was performed to assess the efficacy/safety of a French purified plasma-derived protein C (PC) concentrate in inherited PC deficiency.

MATERIALS AND METHODS

Nine patients were enrolled, five children aged < 5 weeks, among whom four with a severe deficiency were homozygous, and four patients < 37 years with PC levels ranging 14-25%, including one compound heterozygous.

RESULTS

Thirty replacement therapy courses were recorded with mean PC dosages ranging between 24-90 IU/kg/day for prophylactic courses and 51-209 IU/kg/day for treatment courses. Recoveries varied between 0.8 and 1.12% IU/kg in preventive situations and between 1.09 and 1.91% IU/kg for treatment courses; 23 treatment courses were performed in patients aged 1 day to 18 years, 19 out of 23 treatments resulted in complete recovery with no sequelae. Treatment efficacy was difficult to assess in four out of 23 cases because the thrombotic event was not confirmed in one case and due to late treatment initiation in the three other cases. Seven prophylactic treatments were used either in association of vitamin K antagonists or to prevent thrombotic events due to vitamin K antagonist introduction or withdrawal. The safety assessed during 914 infusions was excellent. No abnormal bleeding was reported, including with high doses, during surgery, with heparin therapy.

CONCLUSIONS

Replacement therapy with this French PC concentrate is safe and effective in patients with inherited PC deficiency.

Prospective evaluation of the '4Ts' score and particle gel immunoassay specific to heparin/PF4 for the diagnosis of heparin-induced thrombocytopenia

BACKGROUND

Heparin-induced thrombocytopenia (HIT) is a severe disease that is often difficult to diagnose. A clinical scoring system, the '4Ts' score, has been proposed to estimate its probability before laboratory testing, and a particle gel immunoassay (H/PF4 PaGIA) has also been developed for rapid detection of HIT antibodies.

AIM

To evaluate the performance of both methods when HIT is suspected clinically.

METHODS

Two hundred thirteen consecutive patients were included in four centers. The probability of HIT was evaluated using the 4Ts score blind to antibody test results. HIT was confirmed only when the serotonin release assay (SRA) was positive.

RESULTS

The risk of HIT was evaluated by the 4Ts score as low (LowR), intermediate (IR) or high (HR) in 34.7%, 60.6% and 4.7% of patients, respectively. The negative predictive value (NPV) of the 4Ts score was 100%, as the SRA was negative in all LowR patients. PaGIA was negative in 176 patients without HIT (99.4%, NPV) and the negative likelihood ratio (LR-) was 0.05. PaGIA was positive in 37 patients, including 21 with HIT (positive predictive value = 56.8%), with a positive LR of 11.4. A negative PaGIA result decreased the probability of HIT in IR patients from 10.9% before assay to 0.6%, whereas a positive result did not substantially increase the likelihood for HIT.

CONCLUSION

The use of the 4Ts score with PaGIA appears to be a reliable strategy to rule out HIT.

Heparin-induced thrombocytopenia: a frequent complication after cardiac surgery

Thrombocytopenia is a common problem in cardiovascular patients, and heparin-induced thrombocytopenia (HIT) is therefore frequently suspected. Unfractionated heparin during cardiopulmonary bypass is particularly immunogenic as 25% to 50% post-cardiac surgery patients develop heparin-dependent antibodies but only 1 to 3% will develop HIT. These antibodies recognize a 'self protein', platelet factor 4 (PF4), bound to heparin. Antibodies associated with a high risk of HIT are mainly IgG1 which strongly activate platelets and coagulation, thereby causing thrombocytopenia and thrombosis. A biphasic evolution of platelet count with a secondary decrease after a previous increase following CPB or non-recovery of thrombocytopenia within 6 days post-operatively always requires screening for HIT antibodies. Both functional (platelet activation tests) and immunologic assays (antigen assays) are necessary in every patient to establish the diagnosis of HIT. When the clinical probability of HIT is high, the first requirement is to discontinue heparin, without waiting for results of laboratory investigations. An alternative anticoagulant such as danaparoid sodium (Orgaran) or lepirudin (Refludan) must then be administered since heparin withdrawal alone is insufficient to control the prothrombotic state associated with HIT. The risk of HIT will probably soon decrease due to the wider use of fondaparinux, which does not interact in vitro with PF4, but it could remain significant in patients undergoing cardiac surgery with CPB.

Improved PCR method for amplification of GC-rich DNA sequences

Most housekeeping genes, tumor-suppressor genes, and approx 40% of tissue-specific genes contain G+C sequences in their promoter region that were very difficult to amplify. In this report, we propose an improved polymerase chain reaction (PCR) method to be used for successful amplification of the tissue factor pathway inhibitor (TFPI)-2 gene promoter region that exhibit >70% G+C content in a sequence of approx 300 bp and a complete CpG island region spanning exon 1, the three transcription initiation sites, and the translation start site. Therefore, this method can be recommended to amplify other GC-rich genomic templates.