Performance of a Mixing Study, continued

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The page below is a sample from the LabCE course Detecting and Evaluating Coagulation Inhibitors and Factor Deficiencies. Access the complete course and earn ASCLS P.A.C.E.-approved continuing education credits by subscribing online.

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Performance of a Mixing Study, continued

Step Two
The next step is retesting 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 test results.
Step Three
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 three 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.