Hello George! Our laboratory would like to start offering the factor inhibitor assay (Bethesda titer). We currently do special coagulation tests for several hospitals and clinics. I was wondering if there is a procedure you are willing to share. Sincerely, Maria E. Martinez, BS MT (ASCP), Senior Medical Technologist–Coagulation, Orlando Regional Medical Center.
Hello, Maria, and thank you for your question. There is a generalized protocol in the Esoterix Coagulation Handbook, 2002, written by Dorothy (Adcock) Funk, MD, Rebecca Jensen, MT (ASCP), Cindy Johns, MT (ASCP)SH, and Paige Macy, MT (ASCP). It may be that Esoterix still distributes copies of the handbook, but I don’t see it on their web site. Given that it may no longer be in print, here is their procedure:
“Serial dilutions are made of patient plasma with veronal buffered saline, then mixed 1:1 with normal plasma containing 100% factor VIII activity and are then incubated for 2 hours. A partial thromboplastin time (PTT)-based factor assay using factor-depleted plasma is then performed on the incubated mixtures. Results are compared to those of incubated normal plasma. One Bethesda unit is defined as the inverse of the dilution that neutralizes 0.5 (50%) of the factor being assayed.”
For a specific step-wise protocol, you may wish to contact the company whose coagulometer you are using, as the methods are instrument-specific. They are likely to provide the method in their manual or accompanying materials, and will provide assistance in setting up your assay.