The global assays assess the interaction of procoagulants and anticoagulants on the generation of thrombin. These assays, as functional tests, may reflect the bleeding tendency in patients with haemophilia better than the conventional assays.
Design and Methods:
In this study the use of three global assays including rotational thromboelastometry (ROTEM®), thrombin generation test (TGT), and clot waveform analysis were evaluated on a cohort of haemophilia A (HA) and haemophilia B (HB) patients. The global assay parameters were compared to the conventional assays and the most sensitive parameters correlated with the clinical phenotype of haemophilia patients.
Results and discussion:
The modified ROTEM® analysis initiated by a minute amount of tissue factor proved to be useful in assessing haemophilia patients. A strong correlation was found between the Maximum Velocity (MaxVel) parameter of ROTEM® and the factor VIII level of haemophilia individuals. The use of corn trypsin inhibitor (CTI) to inhibit contact pathway improved the sensitivity and specificity of the ROTEM® analysis. A significant difference between the TGT parameters of patients groups and the control was noted. The use of CTI improved the sensitivity and specificity of the test, in particular peak height in platelet rich plasma (PRP) samples. The results in PRP+CTI group showed that platelets play an important role in heterogeneity of thrombin generation amongst severe haemophilia patients where the relevant deficient factor is < 1.0 IU/dL compared to conventional clotting assays.
In clot waveform analysis, this study showed a better correlation between the velocity indices of the APTT test (Min1 and Min2) and the FVIII activity of HA individuals compared to the correlation between the APTT test itself and the FVIII activity level. The Min1 and Min2 appear to be more sensitive, simple, fast and cost effective in the diagnosis of hypocoagulability, and monitoring of haemophilia patients compared to the conventional tests.
The area under the thrombin generation curve (AUC), peak height (PH), and time to peak (TP) parameters of the in-house TGT in PRP+CTI test category showed a strong correlation with patient age at first joint bleed (r = 0.693 p = 0.003, r = 0.718 p = 0.002, and r = -0.703 p = 0.002 respectively). The type of F8 mutation was also correlated with the patient’s thrombin generation capacity. Based on two ubgroups of null mutations and non-null mutations, the PH and AUC in PPP+CTI category showed a significant increase in the non-null mutation group. The time to the maximum velocity of ROTEM® (tMaxVel) was also shorter in the non-null mutation group.
The use of global assays in diagnosing hypocoagulability, and monitoring haemophilia patients proved to be useful, especially in areas where conventional methods are not responsive. However, the multifactorial dependency of global assays make them difficult to interpret on their own, therefore, these assays should be used in parallel with the conventional tests in order to be more useful.
|Date of Award||May 2011|
|Supervisor||Edward Tuddenham (Supervisor)|