Laboratory Aspects

The haemostatic process is characterized by a series of biochemical reactions aiming at preventing blood loss through blood clot formation. This latter process is mediated by the interaction of platelets on the surface of the injured vessel wall which in turn induces the coagulative phase requiring the activation of inactive zymogen into active proteases. Haemophilia A and B are rare disorders in which the coagulation cascade is affected due to the lack of blood clotting FVIII and FIX, respectively. In order to provide the appropriate therapy for patients with these bleeding disorders, several laboratory tests have to be performed. The initial screening is conducted by screening global tests such as prothrombin time (PT) and activated partial thromboplastin time (aPTT) but only this latter is prolonged in hemophilia. Next, the measurement of factor activity is required for the diagnostic assessment and classification of the disease severity. Three methods can be performed for evaluating FVIII activity including one-stage, two-stage and chromogenic assays. Approximately 30% of severe Haemophilia patients develop FVIII inhibitors which neutralize the clotting activity. The most common assay employed for the detection of inhibitors is the Bethesda assay that combines plasma containing normal amount of FVIII with same volume of patient plasma. Problems in Haemophilia diagnosis or inhibitor detection can occur at any stage in the clinical diagnosis/laboratory phase, from the pre-analytical to the analytical to postanalytical. Therefore, the aim of this chapter is to summarize the diagnostic approaches, pitfalls and interpretation of coagulation assay in Haemophilia.

Keywords: Clotting factor, Haemostasis, Haemophilia, Inhibitors assays, Laboratory test.