Differential Diagnosis for High aPTT with Normal PT and Normal INR

Single Most Likely Diagnosis

• Lupus Anticoagulant: This is a common cause of an isolated prolonged aPTT. Lupus anticoagulant is an antibody that interferes with the coagulation cascade, leading to an increased aPTT. It is often seen in patients with autoimmune disorders, such as systemic lupus erythematosus, but can also be present in otherwise healthy individuals.

Other Likely Diagnoses

• Heparin Therapy: Heparin is an anticoagulant that primarily affects the intrinsic coagulation pathway, leading to an increased aPTT. Patients on heparin therapy, especially those with therapeutic or high doses, can present with a prolonged aPTT.
• Factor Deficiencies (Factor VIII, IX, XI, XII): Deficiencies in these factors, which are part of the intrinsic coagulation pathway, can lead to an isolated prolongation of the aPTT. These deficiencies can be congenital or acquired.
• Von Willebrand Disease: This condition, characterized by a deficiency or dysfunction of von Willebrand factor, can lead to an increased aPTT due to its role in the stabilization of factor VIII.

Do Not Miss Diagnoses

• Disseminated Intravascular Coagulation (DIC): Although DIC typically presents with both prolonged PT and aPTT, early stages or specific types of DIC might initially present with an isolated prolongation of the aPTT. Missing this diagnosis can be catastrophic due to its high mortality rate if left untreated.
• Sickle Cell Disease: In some cases, sickle cell disease can lead to an increased aPTT due to chronic activation of the coagulation system and possible factor deficiencies. It's crucial not to miss this diagnosis due to its significant implications for patient management.

Rare Diagnoses

• Factor XIII Deficiency: This is a rare bleeding disorder that can affect the coagulation cascade, potentially leading to an increased aPTT, although it more commonly presents with clot instability.
• Acquired Hemophilia A: This is a rare condition where autoantibodies against factor VIII lead to its deficiency, resulting in an increased aPTT. It can occur in patients with no previous history of bleeding disorders.
• Paroxysmal Nocturnal Hemoglobinuria (PNH): PNH is a rare, acquired, life-threatening disease of the blood characterized by the destruction of red blood cells, activation of the coagulation system, and an increased risk of thrombosis. It might occasionally present with coagulation abnormalities, including an isolated prolongation of the aPTT.