I have a question about the post regarding mixing studies and CAP checklist question 37991. (I have been trying to post this on “The Fritsma Factor” with no success.)
I thought CAP question 37991 addressed appropriate plasma for mixing studies. If this is the case, is it appropriate to use lyophilized plasma for mixing? I thought that practice was discouraged.
If the post is referring to controls for mixing studies, do you think that is required? I remember a CAP posting from years ago (John Brandt) that said since the testing is really PT or APTT based, your usual PT/APTT controls should suffice; you would not need to run specific controls for the mixing studies.
Thank you for clarification (and “The Fritsma Factor”)
Nancy, thank you for your comment. You can post comments directly to Fritsma Factor using the “Comment” button, however I watch for e-mails and am happy to post them as a blog entry.
By using the term “control” I could be confusing the mixing study issue. Dr. Brandt is correct, we don’t actually run a control parallel to the patient specimen as we conduct a mixing study. The “control plasma” used in mixing studies could be properly named “pooled normal plasma.” As I mentioned in the previous post, it should consist of plasma from at least 20 screened normal male and female donors aged 18 to 66.
CAP doesn’t specify, but we agree the plasmas should be platelet-free (less than 10,000/uL) and should be collected in the same anticoagulant as the patient specimen, usually 3.2% (0.109 M) trisodium citrate. CAP does not appear to prohibit using lyophilized plasma, although we prefer commercially prepared frozen plasma.
Of course, you can prepare your own pooled normal plasma, however the commercial plasmas are screened for viruses and prepared using GMP and are tested to ensure all coagulation factors are within the reference interval. Geo
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