Differential Diagnosis for Raised aPTT

The following differential diagnosis is organized into categories to help prioritize potential causes of a raised activated partial thromboplastin time (aPTT).

• Single Most Likely Diagnosis

  • Heparin therapy: This is a common and well-known cause of elevated aPTT. Heparin works by activating antithrombin, which then inhibits thrombin and other clotting factors, leading to an increase in aPTT.

• Other Likely Diagnoses

  • Lupus anticoagulant: This is an antibody associated with autoimmune disorders that can interfere with phospholipid-dependent clotting tests, leading to a prolonged aPTT.
  • Factor deficiencies (e.g., factor VIII, IX, XI, XII): Deficiencies in these clotting factors can result in an increased aPTT due to impaired coagulation cascade.
  • Vitamin K deficiency: Vitamin K is essential for the production of clotting factors. A deficiency can lead to an increase in aPTT due to decreased production of these factors.
  • Warfarin therapy: Although warfarin primarily affects the prothrombin time (PT), it can also prolong the aPTT, especially at higher doses.

• Do Not Miss Diagnoses

  • Disseminated intravascular coagulation (DIC): This is a serious condition characterized by both clotting and bleeding. It can cause a prolonged aPTT due to consumption of clotting factors.
  • Sepsis: Severe infections can lead to coagulopathy, including an increase in aPTT, due to the activation of coagulation pathways and consumption of clotting factors.
  • Hemophilia A or B: These are genetic disorders leading to deficiencies of factor VIII or IX, respectively. They can cause significant prolongation of aPTT and are critical to diagnose due to their implications for treatment and management.

• Rare Diagnoses

  • Factor inhibitors (e.g., factor VIII inhibitors): These are rare antibodies that can develop against specific clotting factors, leading to their inactivation and a prolonged aPTT.
  • Paroxysmal nocturnal hemoglobinuria (PNH): A rare, acquired, life-threatening disease of the blood characterized by the destruction of red blood cells, activation of coagulation, and an increased risk of thrombosis, which can lead to an elevated aPTT.
  • Congenital coagulopathies (other than hemophilia A and B): These include rare deficiencies of other clotting factors and can present with a prolonged aPTT.