Which statement correctly identifies the laboratory pattern seen in both Hemophilia A and Hemophilia B?

Which statement correctly identifies the laboratory pattern seen in both Hemophilia A and Hemophilia B?

• A. Low platelets.
• B. Elevated d-dimer.
• C. Prolonged PT with normal aPTT.
• D. Prolonged aPTT with normal PT.

Answer: (D)

Hemophilia A and Hemophilia B involve deficiencies in factors of the intrinsic coagulation pathway. The intrinsic pathway is what the aPTT measures, while the PT assesses the extrinsic pathway. When factors VIII or IX are deficient, the intrinsic pathway is slowed, so the aPTT becomes prolonged, but the PT remains normal because the extrinsic pathway (and factor VII) is unaffected. That combination—prolonged aPTT with a normal PT—is the classic lab pattern for these hemophilias. Other patterns don’t fit: low platelets point to a platelet problem, not a coagulation-factor defect. Elevated d-dimer suggests active fibrinolysis or thrombosis, not a simple factor deficiency. Prolonged PT with normal aPTT would indicate an extrinsic pathway issue (like a VII deficiency or vitamin K–dependent factor deficiency), not hemophilia.

Hemophilia A and Hemophilia B involve deficiencies in factors of the intrinsic coagulation pathway. The intrinsic pathway is what the aPTT measures, while the PT assesses the extrinsic pathway. When factors VIII or IX are deficient, the intrinsic pathway is slowed, so the aPTT becomes prolonged, but the PT remains normal because the extrinsic pathway (and factor VII) is unaffected. That combination—prolonged aPTT with a normal PT—is the classic lab pattern for these hemophilias.

Other patterns don’t fit: low platelets point to a platelet problem, not a coagulation-factor defect. Elevated d-dimer suggests active fibrinolysis or thrombosis, not a simple factor deficiency. Prolonged PT with normal aPTT would indicate an extrinsic pathway issue (like a VII deficiency or vitamin K–dependent factor deficiency), not hemophilia.