Final answer:
The primary reagents used in the intrinsic pathway of the activated parietal thromboplastin time include a surface activator for factor XII, phospholipids, and calcium chloride. These reagents initiate a cascade that leads to the activation of various factors, culminating in the formation of a fibrin clot.
Step-by-step explanation:
Activated Partial Thromboplastin Time (aPTT) Reagents
The activated partial thromboplastin time (aPTT) is a test that measures the efficacy of the intrinsic and common coagulation pathways. The primary reagents used in this test include a surface activator that activates factor XII (the Hageman factor), phospholipids which provide a surface for the assembly of the coagulation factor complexes, and calcium chloride to overcome the chelation effect of anticoagulants used in blood collection.
In the intrinsic pathway, when factor XII comes in contact with negatively charged surfaces, like kaolin, silicates, or ellagic acid, it initiates a cascade of activation: factor XII activates factor XI, which activates factor IX, and combined with factor VIII, activates factor X leading to the common pathway. Platelet factors and endothelial cells also contribute to these reactions, accelerating the activation process. The common pathway then follows, involving the conversion of prothrombin to thrombin, which eventually results in fibrin clot formation.
Calcium is an essential component as it is necessary for the proper function of several steps in the coagulation cascade. For aPTT testing, blood samples are commonly collected in tubes containing EDTA as an anticoagulant, which is later neutralized by calcium in the reagent mix. The test's outcome is influenced by various factors, such as the presence of coagulation inhibitors, levels of coagulation factors, and the function of fibrinolysis mechanisms including plasmin.