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More on Mixing Studies

Here is additional information on mixing studies provided by John Olson, MD, who is a “seasoned” CAP inspector. Dr. Olson cautions that he is not speaking for CAP, but providing his expert opinion. He cites CAP HEM.37991, Mixing Studies Procedure: When plasma-mixing studies are performed, an appropriate pooled plasma is utilized. NOTE: It is not appropriate to use single patient plasma samples with normal PT/aPTT values as the “normal” plasma reagent, as factor levels may vary over a wide range without affecting PT/aPTT results. Pooled plasma prepared in the laboratory or commercial products comprised of at least 20 apparently healthy donors are acceptable. Evidence of Compliance: Written procedure for local preparation of pooled plasma for plasma-mixing studies using at least 20 healthy donors OR written procedure describing the use of a commercial product comprising at least 20 healthy donor.

  • Kaczor DA, et al. Evaluation of different mixing study reagents and dilution effect in lupus anticoagulant testing. Am J Clin Pathol 1991;95:408–11.
  • Clinical and Laboratory Standards Institute (CLSI). One-Stage Prothrombin Time (PT) Test and Activated Partial Thromboplastin Time (aPTT) Test; Approved Guideline-Second Edition. CLSI Document H47-A2. (ISBN 1-56238-672-7). Clinical and Laboratory Standards Institute, 940 West Valley Road, Suite 1400, Wayne, PA 19087-1898,  USA, 2008.

Dr. Olson adds, “Thus, either commercial or locally prepared pools are acceptable. The pool is better with larger numbers but, as stated, requires at least 20 apparently health donors. A lab should be sure that the plasma pool is appropriately anticoagulated (0.109M citrate) and not some other formulation of citrate like ACD or CPD. I hope this helps.

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