Which statement correctly describes PT/INR and aPTT in coagulation assessment?

Which statement correctly describes PT/INR and aPTT in coagulation assessment?

• A. PT/INR evaluates the extrinsic pathway; aPTT evaluates the intrinsic pathway.
• B. PT/INR evaluates the intrinsic pathway; aPTT evaluates the extrinsic pathway.
• C. PT/INR and aPTT assess the same pathway.
• D. PT/INR measures platelet function; aPTT measures fibrinogen levels.

Answer: (A)

PT/INR and aPTT are used to screen different parts of the coagulation cascade. PT/INR mostly reflects the extrinsic pathway, which is triggered by tissue factor and depends on factor VII (and the common pathway factors II, V, and I to a lesser extent). aPTT, on the other hand, assesses the intrinsic pathway, which involves factors XII, XI, IX, and VIII, also testing the common pathway factors. Because they target different pathways, they provide complementary information about how well the blood can form a clot. This is why the statement that PT/INR evaluates the extrinsic pathway and aPTT evaluates the intrinsic pathway is the best description. The other option suggesting they assess the same pathway, or proposing that PT/INR measures platelet function or fibrinogen levels, does not fit how these tests are designed or what they measure.

PT/INR and aPTT are used to screen different parts of the coagulation cascade. PT/INR mostly reflects the extrinsic pathway, which is triggered by tissue factor and depends on factor VII (and the common pathway factors II, V, and I to a lesser extent). aPTT, on the other hand, assesses the intrinsic pathway, which involves factors XII, XI, IX, and VIII, also testing the common pathway factors. Because they target different pathways, they provide complementary information about how well the blood can form a clot.

This is why the statement that PT/INR evaluates the extrinsic pathway and aPTT evaluates the intrinsic pathway is the best description. The other option suggesting they assess the same pathway, or proposing that PT/INR measures platelet function or fibrinogen levels, does not fit how these tests are designed or what they measure.