What laboratory finding is characteristic of factor VII deficiency?

In factor VII deficiency, the laboratory finding that is characteristic is an increased prothrombin time (PT). Factor VII is a vitamin K-dependent plasma protein that plays a crucial role in the extrinsic pathway of the coagulation cascade. Its primary function is to initiate blood coagulation in response to tissue injury.

When factor VII is deficient, the extrinsic pathway is impaired, leading to delays in the formation of thrombin and subsequent fibrin clot formation. As a result, the prothrombin time becomes prolonged, reflecting this deficiency in the extrinsic pathway.

Increased bleeding time may be seen with platelet-related disorders, but it does not specifically relate to factor VII deficiency. A decreased platelet count is indicative of thrombocytopenia, which is not a direct effect of factor VII deficiency. Increased partial thromboplastin time (PTT) is more associated with deficiencies in the intrinsic pathway factors, such as factor VIII or IX, rather than factor VII, which affects the extrinsic pathway. Therefore, an increased prothrombin time remains the hallmark laboratory finding for factor VII deficiency.