APTT and PT are prolonged; which pathways are affected?

APTT and PT are prolonged; which pathways are affected?

• A. Intrinsic and extrinsic pathways
• B. Intrinsic only
• C. Extrinsic only
• D. Neither

Answer: (A)

PT evaluates the extrinsic pathway (and the common pathway), while APTT evaluates the intrinsic pathway (and the common pathway). When both tests are prolonged, it means factors shared by both tests—the common pathway—are affected, or there are multiple factor deficiencies spanning both pathways. In other words, both intrinsic and extrinsic pathways appear compromised. If only one test were prolonged, that would point to a problem in just that pathway (extrinsic for PT alone, intrinsic for APTT alone).

PT evaluates the extrinsic pathway (and the common pathway), while APTT evaluates the intrinsic pathway (and the common pathway). When both tests are prolonged, it means factors shared by both tests—the common pathway—are affected, or there are multiple factor deficiencies spanning both pathways. In other words, both intrinsic and extrinsic pathways appear compromised. If only one test were prolonged, that would point to a problem in just that pathway (extrinsic for PT alone, intrinsic for APTT alone).