mixing study schematic no numbers LC 2016
The next step is a retesting of the PT and/or aPTT test with the newly created sample mixture. The results should be documented on a worksheet to compare to the original PT and/or aPTT tests.
The sample that has been made for the mixing study consisting of the pooled normal plasma and the patient plasma should also be incubated to rule-out any slow reacting inhibitors. To do this the "mixed" specimen is incubated at 37º C for 1-2 hours or as long as required by your laboratory's procedure. A set of control tubes should also be incubated at the same time as the mixed sample tube. A pure patient plasma sample and a pure pooled normal plasma sample will serve as the controls in this procedure. You may incubate all 3 tubes together in a water bath or heat block. Refer to the image on the right. The incubation of these controls will account for the heat-labile state of some coagulation factors which will be discussed again.
After the incubation phase, the PT and/or aPTT tests should then be repeated once more. If any coagulation inhibitors were present in the patient sample, the incubation phase would have given the ideal temperature and time for the antibody-coagulation factor reaction to take place. This is especially helpful in the case of anti-factor VIII inhibitors since they are often slow acting or weak inhibitors.