Differential Diagnosis for Normal Fibrinogen but High PTT

• Single Most Likely Diagnosis
  • Lupus Anticoagulant: This is a common cause of an isolated prolonged PTT with normal fibrinogen levels. Lupus anticoagulant is an antibody that interferes with the coagulation cascade, leading to an increased PTT. It is often seen in patients with autoimmune disorders, such as systemic lupus erythematosus.
• Other Likely Diagnoses
  • Factor XII Deficiency: Factor XII deficiency is another possible cause of an isolated prolonged PTT. Factor XII is involved in the intrinsic coagulation pathway, and its deficiency can lead to an increased PTT.
  • Factor XI Deficiency: Similar to Factor XII, Factor XI deficiency can also cause an isolated prolonged PTT due to its role in the intrinsic coagulation pathway.
  • Heparin Effect: Recent or ongoing heparin therapy can cause an elevated PTT, even if fibrinogen levels are normal.
• Do Not Miss Diagnoses
  • Disseminated Intravascular Coagulation (DIC): Although DIC typically presents with abnormalities in multiple coagulation parameters, including fibrinogen, it can occasionally present with an isolated prolonged PTT. Missing DIC can be catastrophic, as it requires prompt treatment.
  • Sickle Cell Disease: Sickle cell disease can cause an elevated PTT due to chronic activation of the coagulation system. While not the most common cause, it is a diagnosis that should not be missed due to its significant clinical implications.
• Rare Diagnoses
  • Factor VIII or IX Inhibitors: The presence of inhibitors against Factor VIII or IX can lead to an elevated PTT. This is a rare condition but is important to consider, especially in patients with a history of hemophilia or recent exposure to factor concentrates.
  • Dysfibrinogenemia: This is a rare condition characterized by the presence of abnormal fibrinogen that functions poorly in coagulation, potentially leading to an elevated PTT despite normal fibrinogen levels.