Coagulation studies

Last updated: Wednesday, 05, December, 2007

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Item Process
Specimen

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

Method

See Activated partial thromboplastin time and Prothrombin time.

Other coagulation screening tests could include Thrombin time, Fibrinogen, and D-Dimer test.

Application

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.

Interpretation

Normal results do not exclude a clinically significant bleeding disorder. False positive results are common.

See individual tests for interpretation of validated abnormal results.

Reference

Eisenberg JM et al. Arch Surg 1982; 117: 48-51.

McPherson J and Street A. Aust Prescriber 1995; 18: 38-41.

Favoloro EJ. Aust J Med Sci 1994; 15: 39-45.