Final answer:
In severe hemophilia B, the activated partial thromboplastin time (aPTT) will be prolonged due to the deficiency of clotting factor IX.
Step-by-step explanation:
In patients with severe hemophilia B, there is an inadequate production of clotting factors, specifically factor IX. This deficiency leads to abnormal laboratory tests associated with the coagulation cascade. The activated partial thromboplastin time (aPTT) will be prolonged because aPTT assesses the integrity of the intrinsic and common pathways, both of which require factor IX. Bleeding time, which tests platelet function, is typically normal in hemophilia. D-dimer levels, which are elevated in cases of active clot breakdown, are not elevated in hemophilia unless there is concurrent clotting and fibrinolysis. Prothrombin time (PT), which tests the extrinsic and common pathways, is typically normal in isolated hemophilia B since these pathways do not rely on factor IX. Therefore, the abnormal lab test in patients with severe hemophilia B is the activated partial thromboplastin time, or aPTT.
The lab test that will be abnormal in patients with severe hemophilia B is the Activated partial thromboplastin time (APTT).
Hemophilia is a genetic disorder that results in a deficiency of clotting factors, specifically factor IX in hemophilia B.
The APTT measures the time it takes for blood to clot and is prolonged in patients with hemophilia B due to the lack of clotting factor IX.