Factor
Identification by Substitution - 1
Specimen requirements:
Fresh whole blood collected in
sodium citrate at a 9:1 ratio of blood to anticoagulant
Principle:
The abnormal test (either PT or
aPTT) is repeated using a 1:1 dilution of patient plasma with the following plasmas:
Normal plasma
Tested within 2 hours or stored at
-20oC for 2 – 5 days
Absorbed plasma
A correction (shortening of time) of
abnormal test indicates that the added plasma contains the missing factor
Aged serum