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.
The patient's plasma is mixed with an equal volume of pooled normal plasma to perform the test, and then a PT and aPTT are conducted off the mixture. Testing is performed on the "mix" with and without an incubation period. The incubated sample is essential to detect the presence of time/temperature-dependent inhibitors.
If adding 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. An inhibitor may be present if the results are not “corrected” or returned to the normal range after adding pooled normal plasma.
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.
