From Louise Pleiss, MT (ASCP), Southcoast Medical Group: We recently changed our mixing study procedure to include rerunning of the normal pooled plasma (NPP) after a 2 hour incubation as one of our system controls, but we are having a difference of opinion about what should happen to the NPP. One site says that the partial thromboplastin time (aPTT, PTT) will increase to about 42 s due to heat labile factors. Our site does not agree and we think we should get nearly the same value as when we first ran the NPP before incubation. Do you have any data to support either side? Thank you.
Hello, Louise and thank you for your question. I agree with your outside site, though they may be overestimating the degree of prolongation. You should expect your normal control plasma clotting time to lengthen by two or three seconds during a 2-hour incubation at 37°C as factor VIII activity becomes reduced. Among other references, Domen RE. Labile coagulation factor activity in pooled random donor platelet concentrates. South Med J. 1988;81:418 indicates the degree of factor VIII activity loss during incubation. The best approach is to compare the PTT result of the incubated NPP-test plasma mix with the PTT result of the incubated, and not the initial NPP to determine correction. Please feel free to follow up with any questions or additional data. Geo.