Summary
A very sensitive and highly reliable test system for the detection of activated coagulation
factor IX (FIXa) has been established. This assay system is based on the cleavage
of a fluorogenic substrate by activated factor X (FXa) which is generated by FIXa.
This assay can be used to process a large number of samples at a time and, being based
on the convenient microtiter plate format, can easily be adapted to automated processing
for routine screening of large sample numbers.
With this assay at hand we determined the FIXa content of different commercially available
therapeutic FIX sources, such as high purity FIX (HPFIX) and prothrombin complex concentrates
(PCC). Here we demonstrate that PCC from several suppliers do not contain significantly
higher levels of FIXa as compared to HPFIX from the same supplier. In fact, there
is a tendency for HPFIX to contain more FIXa than PCC. Moreover, HPFIX from certain
manufacturers who do not produce PCC are characterized by an exceptionally high content
of FIXa. Therefore, the higher thrombogenic potential of PCC which is well documented
clinically cannot be explained solely – if at all – by an increased content of FIXa.
Rather, it will be necessary to identify other components responsible for this phenomenon.