Differential Diagnosis

The patient's laboratory results show an elevated PT (18.1 s) and aPTT (39.8 s) with a normal fibrinogen level (256 mg/dL) and platelet count (189 x 10^3/μL). Based on these results, the differential diagnosis can be categorized as follows:

• Single most likely diagnosis

  • B. Coumadin Therapy or common pathway deficiency: The elevated PT and aPTT with a normal fibrinogen level and platelet count suggest a problem with the common coagulation pathway, which could be due to Coumadin therapy or a deficiency in factors such as factor X or factor II (prothrombin).

• Other Likely diagnoses

  • A. Hemophilia A, B, or other intrinsic factor deficiency: Although the PT is elevated, which is not typical for hemophilia A or B, the significantly elevated aPTT could suggest an intrinsic pathway defect, such as factor VIII or IX deficiency. However, the elevation of PT makes this less likely as the primary diagnosis.
  • C. Heparin therapy: Heparin can cause an elevation in aPTT, and to a lesser extent, PT. However, the degree of elevation in both PT and aPTT, along with the normal thrombin time, makes this less likely compared to Coumadin therapy.

• Do Not Miss (ddxs that may not be likely, but would be deadly if missed.)

  • Disseminated Intravascular Coagulation (DIC): Although not directly suggested by the provided lab results, DIC can cause elevations in PT and aPTT due to consumption of clotting factors. It's a critical condition that requires prompt diagnosis and treatment.
  • Vitamin K deficiency: This could lead to elevations in PT and aPTT due to the deficiency of vitamin K-dependent clotting factors (II, VII, IX, X). It's less likely given the context but should be considered, especially if the patient has a history of malnutrition or malabsorption.

• Rare diagnoses

  • D. von Willebrand’s Disease: Typically presents with an isolated elevation of aPTT due to a deficiency in von Willebrand factor, which is necessary for platelet adhesion and also serves as a carrier for factor VIII. The significant elevation in PT makes this diagnosis less likely.
  • Lupus Anticoagulant: Can cause an elevation in aPTT, but the presence of an elevated PT and the clinical context would make this a less likely primary diagnosis without further testing for antiphospholipid antibodies.
  • Factor deficiencies other than those mentioned (e.g., factor V, combined factor deficiencies): These are rare and would typically present with elevations in both PT and aPTT, depending on the specific factors involved. Detailed factor assays would be necessary to diagnose these conditions.