Which test is the best screening test for hemophilia A, a deficiency of factor VIII?

Which test is the best screening test for hemophilia A, a deficiency of factor VIII?

• A. Partial thromboplastin time
• B. Prothrombin time
• C. Thrombin time
• D. Platelet count

Answer: (A)

Factor VIII deficiency affects the intrinsic coagulation pathway. The partial thromboplastin time evaluates the intrinsic and common pathways, and a deficiency in factor VIII slows the time to clot formation, so the test is prolonged and serves as the most sensitive initial screen for hemophilia A. Prothrombin time targets the extrinsic pathway and often remains normal in isolated factor VIII deficiency. Thrombin time assesses the final step of clot formation, mainly reflecting fibrinogen issues or heparin effect, not a primary factor VIII problem. Platelet count looks at platelets themselves, not the coagulation cascade. Therefore, partial thromboplastin time is the best screening test for detecting hemophilia A.

Factor VIII deficiency affects the intrinsic coagulation pathway. The partial thromboplastin time evaluates the intrinsic and common pathways, and a deficiency in factor VIII slows the time to clot formation, so the test is prolonged and serves as the most sensitive initial screen for hemophilia A. Prothrombin time targets the extrinsic pathway and often remains normal in isolated factor VIII deficiency. Thrombin time assesses the final step of clot formation, mainly reflecting fibrinogen issues or heparin effect, not a primary factor VIII problem. Platelet count looks at platelets themselves, not the coagulation cascade. Therefore, partial thromboplastin time is the best screening test for detecting hemophilia A.