Mixing studies can be performed after an unexpected, prolonged PT or APTT is encountered to determine if the problem stems from a factor deficiency or the presence of an inhibitor.
To perform the test, the patient's plasma is mixed with an equal volume of pooled normal plasma, and then a PT and APTT are performed off the mixture. Testing is performed on the "mix" with and without an incubation period. The incubated sample is important to detect the presence of time/temperature-dependent inhibitors.
If the addition of the pooled plasma brings the resultant values into the normal range, then the pooled plasma contained factors in which the patient's sample was deficient, and the patient has a factor deficiency. If the results are not “corrected” or brought back into the normal range after the addition of pooled normal plasma, then an inhibitor may be present.
If correction has occurred, the next step in the diagnostic sequence of events is to perform a factor assay to determine which specific factor is lacking.
