Elevated aPTT is typically seen in which disorders?

• A. Hemophilia A/B and Von Willebrand disease
• B. Platelet deficiency
• C. Vitamin K deficiency
• D. Dehydration

Answer: (A)

Elevated aPTT points to problems in the intrinsic coagulation pathway, which includes factors VIII, IX, XI, and XII and the common pathway. In hemophilia A (factor VIII deficiency) and hemophilia B (factor IX deficiency), the intrinsic pathway is impaired, leading to a prolonged aPTT. Von Willebrand disease can also prolong the aPTT in some cases because von Willebrand factor stabilizes factor VIII; when VWF is deficient, factor VIII levels can drop, making the aPTT longer, especially in more severe disease. By contrast, platelet deficiency mainly affects bleeding time rather than the coagulation cascade measured by aPTT. Vitamin K deficiency primarily impairs the extrinsic pathway (shortened or prolonged PT/INR), with aPTT only affected in more severe cases, and dehydration does not directly prolong coagulation times.