Confirmation and characterization of factor IX inhibitor
The patient should not be anticoagulated
Do not draw from an arm with a heparin lock or heparinized catheter
Activated partial thromboplastin time (aPTT)-based system. Serial dilutions are made of patient plasma with veronal buffered saline, then mixed with normal plasma containing close to 100% factor IX activity and are then incubated for 2 hours. An aPTT-based factor IX assay using factor IX-depleted plasma substrate is then performed on these incubated mixtures. Results are compared to those of incubated normal plasma. One Bethesda unit is defined as the amount of factor IX inhibitor that neutralized 0.5 IU of factor IX in this system. The number of serial dilutions tested is based on the anticipated level of the inhibitor.
An interpretive report will be provided