Reference Range: Current laboratory (adult, M/F) normal ranges are as follows:
11.7-14.5 Seconds. May be slight batch variation – current ranges always available on APEX.
Min. Volume: Small samples are difficult to process and will only be accepted for small children.
Turnaround Time:
Age of Sample: Samples will be rejected if received more than 8 hours after they are taken for routine clotting, more than 4 hours for D-dimers and more than 1 hour for specialist tests.
Interpretation of Coagulation Screens: Effective haemostasis requires correct functioning of the vessel endometrium, platelets and coagulation proteins. Coagulation screens offer in vivo testing of the coagulation proteins only.The pathways may be affected by several in vivo & in vitro factors .eg underfilling of tubes, incorrect storage and lupus anticoagulants. It is therefore important to interpret screens in the light of then patient’s clinical status.
Pre operative screens: Coagulation screens on pre operative elective patients are performed to identify any undiagnosed bleeding tendency. In the elective, non-hospitalised patient this will be an undiagnosed inherited bleeding disorder e.g. von Willebrand’s disease. In this group of patients it is therefore acceptable to use the results of any previous coagulation screen without the need to repeat the screen within the pre-operative period providing there is no new history of bleeding. Hospitalised or unwell patients should have a recent coagulation screen performed.
Limitations:
  • All coagulation tubes must be mixed several times by gentle inversion immediately after venepuncture. Mixing the sample with the anticoagulant stops the sample clotting within the tube.
  • All coagulation samples must be kept at room temperature.
  • It is not possible to provide accurate results on clotted, insufficient, lipaemic or haemolysed samples. These will be rejected with the appropriate comment.
  • All specialist tests must include all relevant clinical details otherwise these will not be processed.
Analysing Laboratory: Coagulation