Medical Laboratory Scientist (MLS) ASCP Exam 2025 – 400 Free Practice Questions to Pass the Exam

Factor VII deficiency is characterized by an increased prothrombin time (PT) while the activated partial thromboplastin time (aPTT) remains normal. This is due to the specific role of Factor VII in the extrinsic pathway of coagulation. The PT tests the integrity of the extrinsic pathway, which includes Factor VII, along with Factor III (tissue factor) and prothrombin. In patients with Factor VII deficiency, there is an impairment in this pathway, leading to a prolonged PT.

Conversely, the aPTT evaluates the intrinsic pathway, which involves factors such as Factor VIII, Factor IX, and Factor X, among others. Since Factor VII is not part of the intrinsic pathway, its deficiency will not affect the aPTT, resulting in a normal aPTT despite the prolonged PT. This clear delineation between the two pathways allows for distinguishing Factor VII deficiency from deficiencies of other clotting factors involved in the intrinsic pathway, which would typically manifest as a prolonged aPTT as well.