Haemostasis and its abnormalities have been traditionally assessed by plasma clotting times, such as the prothrombin, activated partial thromboplastin and thrombin times. These times depend on the thrombin dependent conversion of fibrinogen to fibrin, but note only the initiation of this process and not its speed or total extent. Factor assays based on these tests have defined the different coagulation disorders including haemophilia[2,3]. While tests have been useful for these purposes, they also have several limitations. These include the fact that all of them are performed under conditions that are far from physiological, and they split the process of coagulation into artificial segments thus not assessing the potential impact of other components of the haemostatic system. Factor assays performed using these tests are limited by their sensitivity at very low levels . Factor levels below 1.0% (0.01 IU/mL) have therefore not been traditionally quantified. In many patients with coagulation disorders, factor assays alone do not correlate well with clinical symptoms. It has been shown that plasma from some patients with severe haemophilia A (HA) has the ability to generate thrombin . The exact basis for this phenomenon is not well understood, but may be related to the balance of levels of different procoagulant and anticoagulant proteins in the blood . It is possible that tests that assess global haemostasis may be better reflective of the clinical features.
Currently, there are no widely available and standardized tests that can quantitatively assess the overall haemostastic potential of blood. The process of thrombin generation and fibrin clot formation can be captured with greater sensitivity and completeness by tests that measure global haemostasis. These include the thrombin generation tests/assay (TGT/TGA) [5,7], thromboelastography(TEG)  and the activated partial thromboplastin time (APTT) waveform analysis (WA)  using different instrument systems. These tests have not only helped in more complete assessment of the process of normal haemostasis but have also provided newer insights into the evaluation of disorders of haemostasis. However, several issues remain to be resolved with regard to standardization of methodology and interpretation of these tests. This study will describe some of these issues with particular reference to hereditary coagulation disorders.