The expected screening test result for a patient with a fibrin stabilizing factor deficiency is which?

• A. Prolonged prothrombin time
• B. Prolonged activated partial thromboplastin time
• C. Prolonged prothrombin time and activated partial thromboplastin time
• D. Normal prothrombin time and activated partial thromboplastin time

Answer: (D)

Fibrin stabilizing factor is factor XIII, which cross-links fibrin strands to make the clot strong. This step happens after the clot has formed, so it does not affect the initial process measured by the standard screening tests. Prothrombin time and activated partial thromboplastin time assess how long it takes to form fibrin, not how well the formed clot is stabilized. Therefore, a deficiency in factor XIII leads to a clot that may break down more easily, but the times to clot formation (PT and aPTT) remain normal. In XIII deficiency, you might look for clot instability with specialized tests like a clot solubility test, but routine screening times are not prolonged. Hence the expected screening result is normal PT and aPTT.