What does partial thromboplastin time (PTT) measure?

Partial thromboplastin time (PTT) is a valuable diagnostic test that specifically evaluates the clotting ability of the intrinsic and common pathways of the coagulation cascade. The intrinsic pathway includes factors involved in the blood's natural clotting process, such as factors XII, XI, IX, and VIII, while the common pathway encompasses factors X, V, prothrombin (factor II), and fibrinogen (factor I) leading to the formation of a fibrin clot.

By measuring PTT, healthcare providers can assess how well these pathways are functioning, which is critical in diagnosing conditions related to bleeding disorders, such as hemophilia or the presence of certain anticoagulants. A prolonged PTT can indicate various issues, including deficiencies in these pathway factors or potential dysfunctions in the circulating anticoagulants affecting the intrinsic clotting mechanism.

The other options do not accurately describe what PTT measures. The extrinsic pathway and common pathways are assessed by Prothrombin Time (PT), and fibrinogen levels are typically measured by fibrinogen assays rather than by PTT. Overall coagulation effectiveness is assessed using more comprehensive tests like the thromboelastogram rather than focusing on specific pathways like PTT does.