NHA Phlebotomy Certification Practice Exam

Which blood component is primarily measured in a prothrombin test?

1. Red blood cells

2. Platelets

3. Clotting factors

4. White blood cells

The correct answer is: Clotting factors

The prothrombin test is primarily used to measure the activity of certain clotting factors in the blood, particularly factors that are dependent on vitamin K, including prothrombin itself, which is also known as factor II. This test helps assess the extrinsic and common pathways of coagulation and is crucial in evaluating the blood's ability to form clots effectively. The measurement of clotting factors is vital in diagnosing conditions related to excessive bleeding or thrombosis and is often used to monitor patients on anticoagulant therapy. Thus, the primary focus on clotting factors in the prothrombin test underscores its role in understanding the coagulation status of an individual. In contrast, the other components listed—red blood cells, platelets, and white blood cells—are not the primary focus of this particular test. Red blood cells are primarily involved in oxygen transport, platelets play a crucial role in the clotting process but are not the specific subject of measurement in the prothrombin test, and white blood cells are mainly related to the immune response. Therefore, the correct answer emphasizes the essential role of clotting factors in the assessment conducted by the prothrombin test.