How does thrombotic thrombocytopenic purpura (TTP) differ from disseminated intravascular coagulation (DIC)?

The choice indicating that activated partial thromboplastin time (APTT) is normal in thrombotic thrombocytopenic purpura (TTP) but prolonged in disseminated intravascular coagulation (DIC) accurately reflects the differences in coagulation profiles associated with each condition.

In TTP, there is typically a microangiopathic hemolytic anemia, which can lead to a decrease in platelets; however, the coagulation pathways remain largely intact, resulting in a normal APTT. This condition is often characterized by a depletion of von Willebrand factor due to an ADAMTS13 deficiency or inhibition, but it does not significantly impact the intrinsic pathway, thus keeping APTT within normal limits.

Conversely, DIC involves widespread activation of the clotting cascade, resulting in the consumption of clotting factors and platelets, leading to both prolonged APTT and prothrombin time (PT). This consumption phenomenon will generally disturb both intrinsic and extrinsic pathways, whereas TTP does not have this widespread clotting scenario.

Overall, understanding these differences in coagulation status is critical for diagnosis and management, illustrating how distinct these two hematological conditions can be in their mechanisms and laboratory findings.