Coagulation studies

4.5 mL blood added to 0.5 mL citrate + 5 mL of EDTA anticoagulated blood.

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:

1. Undue bleeding after cutting or biting the tongue.
2. Significant easy bruising.
3. Prolonged bleeding after dental extractions, or re-bleeding.
4. Prolonged bleeding or excessive bruising after any surgery (major or minor).
5. An adequate menstrual history, including family history of excessive or prolonged menses.
6. Family history of post-op bleeding requiring transfusion.
7. Current or recent medications including: asprin, other analgesics, cold medications, warfarin.

If the screening history is negative, then:

1. No tests are recommended prior to minor surgery.
2. Before major surgery, an APTT, PT, platelet count +/- fibrinogen are recommended.

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.