Monday, December 24, 2012

Tests for coagulation disorders


Tests for coagulation disorders:

Prothombin Time (PT):
PT is the time in seconds that takes the blood to clot. This test result can vary depending on laboratory system used. A longer PT means that the patient’s blood is taking longer to clot.

Fig. BD Vacuitainer tube with Sodium citrate (Sky Blue top)

Activated Partial thromboplastin time (APTT):
APTT is a measure of how well the patient’s blood would clot. A sample of blood is “clot activated” and the time taken to clot is measured in seconds. Like the PT a longer aPTT means that clotting will generally take longer.


International Normalized Ratio (INR):
INR is a standardized PT test. The patient’s blood PT results are compared to an internationally standardized PT sample, and the ratio is reported rather than seconds, this means that INR is usually 1. If INR is 2, this means that the blood will take twice as long to clot and so on.

D-Dimers:
A D-dimer is a fragment of a clot which has been broken by the body in a process called fibrinolysis. It is therefore used in the management of pulmonary embolism and DVT patients.
A high positive result means that there must have been (or still is) a thrombus (clot), although whilst a negative result probably means no thrombus, care should be made to ensure that the patient does not have an impaired fibrinolysis pathway.

This would lead to:

  • Higher risk of thrombus formation initially
  • Inability to break down the thrombus
  • Lack of D-dimers-however the thrombus is still present

False positive are possible with liver disease and post-surgery so this is an example of a test which also requires confirmation from additional studies such as CT scan.

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