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4.5 mL blood added to 0.5 mL citrate + 5 mL of EDTA anticoagulated blood.
Other coagulation screening tests could include Thrombin time, Fibrinogen, and D-Dimer test.
Routinely a full blood count (FBC) is included to assess the adequacy of the platelet count.
The combination of an APTT and a PT as 'screening tests' may not detect clinically significant bleeding disorders; the sensitivity of a detailed clinical assessment is high.
In the pre-operative assessment of patients, these tests should not be routinely performed. However, in a patient with a history of abnormal bruising or bleeding, these tests alone may well be inadequate.
A simple pre-operative screening questionairre could include questions concerning:
If the screening history is negative, then:
If the screening history is positive or if the surgery is likely to impair haemostasis e.g. cardiac surgery, then a coagulation screen is recommended.
Additional testing may be indicated if the history is suspicious for a bleeding diatheses even though the initial screening tests are negative, von Willebrand's disease being the most common cause.
Normal results do not exclude a clinically significant bleeding disorder. False positive results are common.
See individual tests for interpretation of validated abnormal results.
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