Which of the following tests primarily assesses extrinsic and common pathway coagulation factors?

Prothrombin Time (PT) is designed to evaluate the extrinsic and common pathway of coagulation. This pathway includes key factors such as factor VII, which is essential for extrinsic pathway activation, as well as factors X, V, prothrombin (factor II), and fibrinogen, which are part of the common pathway.

When conducting a PT test, a sample of blood is mixed with tissue factor and calcium. The time it takes for a clot to form is then measured. An extended PT indicates a potential deficiency in one or more of the factors involved in these pathways, which could suggest clotting disorders or issues related to vitamin K deficiency.

Understanding the function and assessment provided by PT is crucial for diagnosing various conditions related to coagulation, particularly those that affect the extrinsic and common pathways. In clinical practice, this test is often used to monitor patients on anticoagulant therapy, especially those taking warfarin, as it gives insight into the effectiveness of anticoagulation and helps in adjusting dosages.