From the Guidelines
The answer is aPTT (activated Partial Thromboplastin Time). The aPTT is not associated with the extrinsic pathway of coagulation but rather measures the intrinsic and common pathways. The extrinsic pathway is initiated by tissue factor (TF) which forms a complex with Factor VII, activating it to Factor VIIa, as described in the study by 1. This pathway is assessed by the Prothrombin Time (PT) test. The PT specifically evaluates the function of the extrinsic and common pathways by measuring the time it takes for blood to clot after tissue factor is added to the sample. In contrast, the aPTT measures the intrinsic pathway by using different activators like kaolin, silica, or ellagic acid, which do not involve tissue factor or Factor VII activation, as explained in the study by 1. Understanding these distinctions is important for correctly interpreting coagulation test results and diagnosing bleeding disorders.
Some key points to consider:
- The extrinsic pathway is initiated by tissue factor and is assessed by the Prothrombin Time (PT) test, as mentioned in the study by 1.
- The aPTT measures the intrinsic pathway and does not involve tissue factor or Factor VII activation, as described in the study by 1.
- The coagulation cascade is a complex process that involves the sequential conversion of inactive enzymes into active enzymes, leading to thrombin generation and clot formation, as explained in the study by 1.
- The balance between coagulation and fibrinolysis is crucial for maintaining normal hemostasis, and any imbalance can lead to bleeding or thrombotic disorders, as discussed in the study by 1.
In clinical practice, it is essential to understand the differences between the extrinsic and intrinsic pathways of coagulation and how they are assessed by different laboratory tests, such as PT and aPTT, to provide accurate diagnoses and effective treatment for patients with coagulation disorders.
From the Research
Extrinsic Pathway Association
The extrinsic pathway is triggered when tissue factor, phospholipid, and calcium are added to plasma anticoagulated with citrate 2. The following are associated with the extrinsic pathway:
- Tissue Factor
- Factor VIIa
Intrinsic Pathway Association
In contrast, the intrinsic pathway is initiated when fresh whole blood is placed in a glass tube, activating the contact pathway where FXII is activated 2. The following is associated with the intrinsic pathway and the common pathway:
- aPTT (activated partial thromboplastin time) - used to evaluate the intrinsic and common pathways of coagulation 2, 3, 4, 5, 6
Answer Choice
Based on the information provided, the answer choice that is NOT associated with the extrinsic pathway is:
- aPTT (activated partial thromboplastin time) This is because aPTT is used to evaluate the intrinsic and common pathways of coagulation, not the extrinsic pathway specifically. Prothrombin Time is associated with the extrinsic pathway as it is used to monitor warfarin anticoagulant therapy and is triggered by the extrinsic pathway 2.