A colleague recently contacted George about prothrombin time mixing studies. Apparently, the College of American Pathologists provided a PT mixing study challenge in a recent survey. George discussed PT mixing studies with Fritsma Factor advisers Larry Brace, PhD and Dave McGlasson who helped list reasons for not doing them:
Reasons for not performing a PT mixing study are…
- The combination of prolonged PT and normal PTT leads to a presumed diagnosis of rare congenital factor VII deficiency without need for a mixing study.
- All coagulopathies except VII prolong the PTT, so a PTT mixing study would be the first choice.
- There are few inhibitors that affect prothrombin, V, VII, and X, particularly since we no longer use bovine fibrin glue in surgery.
- The most likely cause for prothrombin, V, VII, and X deficiency is liver disease, and the PT mix doesn’t add much to the diagnosis.
We were unable to find compelling reasons for performing the PT mixing study, so we are inviting you to share your experience.