[How I explore… hémostatic abnormalities in pediatrics]

Hemostasis work-up is frequently requested in pediatric cares and can often seem complicated to interpret when certain results return to be abnormal. In addition, these biological tests are very sensitive and several pre-analytical conditions can influence them and skew the results, leading to erroneous analyzes and diagnoses. Indeed, systemic inflammation, anemia or even only the delay between blood sampling and analysis can make the results more difficult to be interpreted. However, when the tests have been carried out under good conditions, having in mind a few basic knowledge of hemostasis can easily help to first distinguish a pathology of primary hemostasis from a coagulopathy. Secondly, depending on the abnormal biological tests, complementary oriented assays may then be requested, ideally in a laboratory specialized in hemostasis, in order to confirm or rule out a true hemorrhagic pathology.

[Hemophilia : a disease on the move]

Over the last hundred years, the treatment of hemophilia has evolved considerably. To date, its principle is still to prevent the occurrence of hemorrhages by regular intravenous injections of factor VIII or IX concentrate. It allows to reach a life expectancy similar to the general population. The quality of life is constantly improving despite the constraint imposed by the modality and frequency of injections. The main complication remains the development of antibodies that inhibit the administered factors. Concentrates of long-acting factors are now available allowing to limit for example the frequency of injections. A bispecific monoclonal antibody reproducing the action of factor VIII and injectable subcutaneously has recently become available to hemophilia A patients, with the advantage of being effective even in the presence of inhibitors. Other non-substitute products are being studied offering interesting leads. Finally, gene therapy shows promising results, giving hope for access to this therapeutic option in a relatively near future. These advances are, however, a challenge for clinical laboratories, which must adapt their measurement techniques to ensure optimal monitoring. The future is on its way for hemophilia. Treatment remains expensive but it is worth the price.

[Inherited platelet disorders : clinical presentations and diagnostic algorithms]

The diagnosis of inherited platelet disorders (IPD) is a complex task. Indeed, due to their rarity, their wide clinical spectrum (intensity of hemorrhagic symptoms) and the need for specialized biological assays (only performed in reference centers) IPDs can be diagnosed very late. However, it is important to remember the crucial need for early diagnosis in order to avoid the use of unnecessary and potentially harmful treatments for the patient. A thorough personal and family history, a complete physical examination and a simple biological work up (blood count, blood smear and platelet occlusion time) will lead to the suspicion of an IPD. It will then be up to the physician to refer the patient to a specialist in order to complete the diagnostic work up and therefore establishing a definitive diagnosis. Here is a description of the most well-known IPDs and their diagnostic algorithms.

[How to explore… Inherited platelet disorders]

Inherited platelet disorders (IPD) include a set of rare diseases whose diagnosis is often difficult because it requires the use of complex biological assays in specialized centers. They are probably under-diagnosed. Clinicians should consider an IPD when facing a chronic thrombocytopenia resistant to intravenous immunoglobulins (IVIG) and steroids together with a family history of thrombocytopenia. A syndromic thrombocytopenia will be suspected by the family survey and specific clinical signs. The confirmation of the diagnosis will then require the use of specialized biological assays such as platelet aggregation, flow cytometry, electron microscopy, platelet secretion assays, karyotype and molecular biology.

[Oral anticoagulants: new horizons]

Anticoagulation is at the dawn of a new era. Dominated for a long time by heparins and vitamin K antagonists, the anticoagulant arsenal is growing up. With a direct and reversible action targeting specifically thrombin (IIa) or factor Xa, these new synthetic agents, given orally, have large therapeutic windows and predictable pharmacokinetics. Their properties allow them to avoid tight monitoring improving patient comfort and security. Pharmacological studies are promising. Regarding some indications, these new drugs seem better than "classical" anticoagulants either in efficacy or in security terms. However, they increase the hemorrhagic risk and particularly in fragile populations like elderly patients or with renal insufficiency. Only few assays are available in the laboratory to evaluate their effects and no antidote is currently on the market. The way to new anticoagulant therapies is now open. In the future, specific indications of vitamin K antagonists, heparins and these new molecules will have to be determined.

Surgical resection of a sphenoid wing meningioma in a patient with Glanzmann thrombasthenia

Glanzmann thrombasthenia (GT) is a rare autosomal recessive disorder characterized by a deficiency or functional defect of platelet glycoprotein (GP) IIb/IIIa. Physiologically, this platelet receptor mediates aggregation of activated platelets by binding the adhesive proteins, fibrinogen, von Willebrand factor (VWF) and fibronectin. This facilitates attachment and aggregation of platelets at sites of vascular injury. We reported the management of a pterional meningioma resection in a patient with Glanzmann thrombasthenia, with recombinant factor VIIa (rFVIIa - NovoSeven) as haemostatic agent. A 48-year-old woman suffering from Glanzmann thrombasthenia was scheduled for spheno-orbital meningioma en plaque surgery. Because of repeated platelet transfusions, this patient developed isoantibodies against missing GPIIbIIIa and alloantibodies against Human Leukocyte Antigen (HLA) leading to refractoriness to platelet transfusions. We observed that Novoseven offered sufficient haemostasis conditions. Therefore, we noticed a deep vein thrombosis. This imposed us to use low weight molecular heparin despite recent surgery.

[Comparative study of five techniques of preparation of platelet-rich plasma]

AIM OF THE STUDY

Injections of platelet-rich plasma (PRP) constitute a new therapeutic for treating chronic tendinopathies. The injection being carried out in the tendon, the volume of PRP should thus be minimal (to decrease the intratendinous pressure and to minimize pain). This PRP should also have a raised platelet count. The quantity of released growth factors could be related to the system of preparation employed. We thus carried out a comparative study of five techniques of preparation of PRP described in the literature.

MATERIALS AND METHODS

Samples of venous blood were taken among five patients in order to compare five techniques of preparation of PRP: University Hospital of Liège technique, Curasan(®) PRP Kit, Plateltex(®), GPS(®)II and RegenLab(®).

RESULTS

The various techniques make it possible to obtain more important platelet concentration than in blood, with variable volumes (0,3 to 6ml). The number of platelets per microlitre appears higher with Plateltex(®) and obtains smallest volume of PRP. The other techniques also give small volumes except for the GPS(®)II. The number of collected platelets with this technique appears thus higher. The best collect efficiency is obtained with RegenLab(®).

CONCLUSION

The technique Plateltex(®) makes it possible to collect the highest concentration of platelets in the smallest volume available.

[Thrombinography: towards a globalization of coagulation tests]

Thrombin is the key enzyme of coagulation and thrombin generation is the central haemostatic process. Current clotting tests (PT, aPTT) measure the time at which the first fibrin filaments appear after activation of coagulation. Yet, more than 95% of thrombin is generated after clot detection, which underlies the poor sensitivity of usual clotting tests for the detection of many hemorrhagic or thrombotic diseases. Thrombinography measures the kinetics of thrombin generation and inactivation during ex vivo coagulation, in standardized conditions. Thrombin generation is reduced in hemophiliacs and in patients under anticoagulant treatment. Thrombin activity is raised in hypercoagulable states, such as antithrombin deficiency, protein C and S deficiency, factor V Leiden and in women under oral contraceptives. Thrombin generation is delayed but amplified in the presence of lupus anticoagulants. In platelet-rich plasma, thrombin generation detects thrombopathies and von Willebrand disease, and allows monitoring of antiplatelet drugs. Thrombinography allows for a global phenotype of the thrombosis-hemostasis system.