Coagulation screen

• Prothrombin time (PT):

  • Measure of the time taken for blood to clot via the extrinsic pathway
  • INR is a standardised version of this test
  • Factor VII is rarely deficient in isolation this test is a measure of overall clotting factor synthesis or consumption
  • Liver disease
  • DIC
  • Vitamin K deficiency
  • Warfarin levels
• Activated partial thromboplastin time (APTT):

  • Time taken for blood to clot via the intrinsic pathway
  • Like with PT, time will be affected by overall clotting factor synthesis or consumption e.g. DIC, liver failure
  • APTT can indicate issues with factors VIII (and vWF), IX and XI
  • Haemophilia A (factor VIII)
  • Haemophilia B (factor IX)
  • Haemophilia C (factor XI)
  • von Willebrands disease (as vWF pairs up with factor VIII)
• von Willebrand's disease will prolong bleeding time
• Thrombin time:

  • How fast fibrinogen is converted to fibrin by thrombin
  • Prolonged time is either a synthetic issue or consumption issue
  • DIC
  • Liver failure
  • Malnutrition
• All anticoagulants (warfarin, heparins, NOACs) will increase the PT/INR and the APTT
• Antiplatelets, such as clopidogrel (P2Y12 inhibitor) and aspirin, will also cause derangement. These, however, will cause an increase in the overall bleeding time but won’t affect PT or APTT.