Clotting/Coagulation Screen and Interpretation

Clotting/Coagulation screens can be important:

  • In identifying haematological conditions/dysfunction, as well as other systems (in particular, liver dysfunction)
  • In monitoring response to and modifying treatments (in particular, warfarin and heparin)
  • In the work-up of patients who are having invasive procedures (classically surgery, but anything more invasive than venepuncture may require screening)

Most screens measure

  • Prothrombin time (PT; normally 11-13 sec)
  • INR (International normalised ratio; normally 1)
    • INR is essentially a comparison of the patient’s PT against a control PT
    • It can be useful as it varies little between labs and tests, making it particularly good for monitoring a trend in patients PT (e.g. with warfarin use)
  • Activated Partial Thromboplastin Time (aPTT; normal values vary)
    • Measures the time taken for a clot to form when exposed to coagulation factors of the Intrinsic pathway
  • Fibrinogen (1.5-4g/l)

Prolonged PT

  • Vitamin K antagonists e.g. warfarin; or vitamin K deficiency
  • Liver disease (causes a reduction in the production of Vit K dependent clotting factors)
    • Often used as a marker of liver dysfunction in paracetamol overdose
  • DIC

Prolonged aPTT

  • Unfractionated heparin and some other anticoagulants (e.g. fondaparinux)
  • Severe liver disease
  • DIC
  • Von Willebrand disease
  • Haemophilia (A or B)
  • Other rare coagulation factor deficiencies
  • SLE/Antiphospholipid syndrome
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