Coagulation Time-Dependant Inhibitor Screen

Department of Haematology

This test is only performed following discussion with the Consultant Haematologist.
Inhibitors affecting the APTT may act immediately or be time dependent. Normal plasma mixed with plasma containing a time dependent inhibitor will initially have a corrected APTT clotting time. However, after 1-2 hours the correction will be overcome and the clotting time will again become prolonged.
In elderly patients the detection of an unexplained low Factor VIII result in conjunction with a corrected APTT with normal plasma is unlikely to be a result of undiagnosed Haemophilia A or von Willebrands Disease. It is more likely to be due to the presence of a spontaneously produced Factor VIII inhibitor.
Severe Haemophiliacs can produce inhibitors to the Factor VIII treatment they are receiving so should be screened for inhibitors periodically.
Test performed at Oxford Haemophilia centre. This is not a validated in-house test and therefore can only be performed at GRH for research/interest purposes only.

Pre-analysis storage: do not store, send to the laboratory as soon as possible or within 2 hours.
Coagulation tests must be performed on samples taken by clean venesection, and filled to the appropriate level (minimum fill line present on BD bottles).
Overfilled, underfilled and haemolysed samples will give erroneous results and will not be processed.

N/A. The presence or absence of a time-dependant inhibitor will be indicated.