In a 10-year-old male with bruising and deep bleeding, an elevated aPTT that does not correct with a mixing study suggests which diagnosis?

In a 10-year-old male with bruising and deep bleeding, an elevated aPTT that does not correct with a mixing study suggests which diagnosis?

• A. Disseminated intravascular coagulation (DIC)
• B. Hemophilia B
• C. Hemophilia A with factor inhibitor
• D. Von Willebrand disease

Answer: (C)

The key idea is how a mixing study helps tell whether a prolonged aPTT is due to a factor deficiency or the presence of an inhibitor. If you mix patient plasma with normal plasma and the aPTT corrects, it points to a deficiency of an intrinsic pathway factor (like factor VIII or IX). If the aPTT does not correct, it indicates an inhibitor that blocks a factor’s activity, most commonly an antibody against factor VIII in hemophilia A. In this scenario, a child with bruising and deep bleeding fits a hemophilia pattern, and the noncorrection on mixing strongly suggests an inhibitor rather than a pure deficiency. The best-fit diagnosis is Hemophilia A with a factor VIII inhibitor, where an antibody neutralizes FVIII, preventing normal clot formation despite mixing with normal plasma. DIC would usually show broader abnormalities (consumption signs such as low platelets, low fibrinogen, elevated D-dimer) and isn’t defined by a noncorrecting mixing result. Hemophilia B would behave like a pure intrinsic-factor deficiency and typically would correct on mixing. Von Willebrand disease often presents with mucocutaneous bleeding and normally would not produce a noncorrecting mixing study.

The key idea is how a mixing study helps tell whether a prolonged aPTT is due to a factor deficiency or the presence of an inhibitor. If you mix patient plasma with normal plasma and the aPTT corrects, it points to a deficiency of an intrinsic pathway factor (like factor VIII or IX). If the aPTT does not correct, it indicates an inhibitor that blocks a factor’s activity, most commonly an antibody against factor VIII in hemophilia A.

In this scenario, a child with bruising and deep bleeding fits a hemophilia pattern, and the noncorrection on mixing strongly suggests an inhibitor rather than a pure deficiency. The best-fit diagnosis is Hemophilia A with a factor VIII inhibitor, where an antibody neutralizes FVIII, preventing normal clot formation despite mixing with normal plasma.

DIC would usually show broader abnormalities (consumption signs such as low platelets, low fibrinogen, elevated D-dimer) and isn’t defined by a noncorrecting mixing result. Hemophilia B would behave like a pure intrinsic-factor deficiency and typically would correct on mixing. Von Willebrand disease often presents with mucocutaneous bleeding and normally would not produce a noncorrecting mixing study.