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Quick Question Summary: Mixing Studies

Here are the results of our June QQ on Mixing Studies:

When performing a partial thromboplastin time (PTT) mixing study using reagent pooled normal plasma (PNP), what do you use as your correction/non-correction limit?

a. Mixture PTT is within 10% of the PNP PTT result: 9 (14%)
b. Mixture PTT is within 5 seconds of the PNP PTT result: 12 (19%)
c. Mixture PTT is within the PTT reference interval: 34 (53%)
d. Rosner index: 6 (9%)
a. Other: 3 (5%)

The majority agree with comments by Dr. Dorothy Adcock-Funk presented at the 12th Annual Symposium on Hemostasis and Thrombosis by Midwest Coag Hemostasis and Thrombosis Laboratories, May 6 and 7. Dr. Adcock asserted that correction to within the reference interval was the most logical approach. I’ve personally preferred using the 10% rule (a) or the Rosner index (d), both of which normalize on the PNP result, but I am in the minority. Our lack of a standardized approach is a serious source of imprecision in performing mixing studies.

Dr. Adcock also commented there is little to be gained by performing a PTT mixing study when the PTT is just a second or two over the upper limit of the reference interval. That comment is the basis for our July QQ, now posted.

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