During a mixing study, what is a key step that must be completed before incubation?

In a mixing study, performing a PT (prothrombin time) or aPTT (activated partial thromboplastin time) on the mix is a critical initial step that helps determine if the prolonged clotting time observed in a patient sample is due to a specific coagulation factor deficiency or the presence of an inhibitor.

When patient plasma is mixed with normal pooled plasma, aPTT or PT tests are performed on this mixture before any incubation occurs. This step allows for the assessment of the interaction between the patient’s plasma and the normal plasma, which is vital in understanding whether the clotting defect is correctable by the addition of normal factors from the pooled plasma. If the clotting time normalizes, it suggests a factor deficiency; if it remains prolonged, it may indicate the presence of an inhibitor.

While the other options are relevant to the overall mixing study process, they do not precede the key step of performing the PT or aPTT on the mix. Adding calcium chloride is typically part of the protocol after the incubation stage, checking for factor inhibitors is part of the interpretation of results, and preparing a fresh plasma sample is an important practice, but it comes prior to the mixing study rather than being a step to be completed before