Coagulation

Coagulation is an important part of the haemostatis and consists out of plasma proteins which are called coagulation factors. Below are several commonly performed assays listed to measure the extent of coagulation. For additional assays please contact us.

 

 

Activated clotting time (ACT)

The ACT is used during surgery, to determine heparinization. Whole blood is mixed with an activator of the intrinsic clotting system. The clotting time increases from approximately 120 seconds to 800 seconds when heparin is active in high concentrations.

 

Activated Partial Thromboplastin Time (aPTT)

The APTT is a general screening procedure for the detection of coagulation abnormalities. In this assay plasma is recalcified in the presence of an exogenous activator and the time to obtain a stable clot is determined. The APTT is sensitive to deficiencies or abnormalities of the blood coagulation factors VIII, IX, XI, XII, X, V and II, of prekallikrein, high molecular weight kininogen and fibrinogen and of inhibitors of blood coagulation. The APTT is an excellent screening test for the diagnosis of coagulation defects and for the monitoring of hemorrhagic and thrombotic diseases.

 

D-Dimer

Normal blood plasma does not have significant amounts of D-dimer. It is present in the blood in detectable amounts in several conditions, most notably in disseminated intravascular coagulation (DIC), a rare disruption in normal coagulation in which rapid intramicrovascular (within the blood vessels) coagulation occurs at the same time as fibrinolysis (clot dissolution mechanism). The D-dimer test is used to diagnose DIC. It is also frequently used to help diagnose deep-vein thrombosis (clots in veins); pulmonary embolism (clots in the lungs); the thrombosis of malignancy; and sickle cell anemia (a form of anemia characterized by bleeding episodes); and to monitor the effects of thrombolytic drugs. Thrombolytic drugs that may increase D-dimer levels are barbiturates, heparin, streptokinase, and urokinase. Levels of D-dimer will be elevated in these conditions.

 

Thrombin Generation Assay (TGA)

Interactions of blood components in contact with (bio)materials activates the clotting cascade. Activated Factor XII (FXIIa, also known as Hageman factor) initiates the intrinsic pathway. Depending on the surface properties of the (bio)material, the pre-kallikrein and high-molecular weight kininogen system accelerate FXII activation. Downstream, this results in activation of Factor XI (FXIa), Factor IX (FIXa) and Factor X (FXa). Finally, FXa activates prothrombin to thrombin, which converts fibrinogen into fibrin to form a fibrin meshwork. Thrombin will also activate platelets and Factor VIII (FVIIIa) and Factor V (FVa). The activated platelets, which expose negatively-charged phospholipid, further enhance coagulation by supporting the formation of FIXa-FVIIIa and FXa-FVa complexes which dramatically increases the rate of thrombin generation. After initial fibrin-clot formation, ongoing thrombin generation is required to sustain and stabilise the clot.

As thrombin is a key element in the coagulation cascade, its measurement gives direct information about a (bio)materials thrombogenic properties (i.e. its ability to form blood clots). In normal plasma, thrombin is captured into the fibrin meshwork and is rapidly inactivated by antithrombin III or other antiproteases. The short half-life of thrombin hampers its accurate enzymatic determination. Therefore, HaemoScan has designed a new test, the thrombin generation assay (TGA), which is based on a special plasma product that enables the determination of thrombin activity in an incubation medium after this has been exposed to a (bio)material.

 

Thrombin-Antithrombin III Complex (TAT)

The conversion of prothrombin into thrombin is a key event in the coagulation cascade. Thrombin acts on various physiological substrates, which enhances its own formation (positive feedback) and contributes to the formation of stable blood clots in hemostasis but also in thrombotic events (e.g. in reaction to exposure to medical devices or bio-materials).

In the human body thrombin is controlled by the action of antiproteases. Antithrombin III is the most important antiprotease, which reacts as a pseudo-substrate with thrombin to form stable thrombin-antithrombin III complexes (TAT). The concentrations of TAT can be measured quantitatively by enzyme immunoassay. TAT levels are an indicator for activation of the blood clotting system and can be reliably measured under conditions were measurable thrombin activity is absent.