Mixing Studies Using a 4:1 Ratio

From Lester Jones at Triad:

I am trying to find out what is the most effective mixing study ratio for lupus anticoagulants. Currently we are using a 1:1 mix for the DRVVT test. I think that a 1:4 would be better.  What do you recommend?

Hi, Mr. Jones,

Reference labs may apply a 4:1 mix when their PTT mixing study is equivocal at 1:1. A 4:1 mix is four parts patient plasma and one part reagent normal plasma. The 4:1 mix is recommended only as a follow-up, is likely to be more sensitive than 1:1 and could detect a weak lupus anticoagulant. I don’t know of anyone who uses a 4:1 mix for the DRVVT assay, nor have I seen it recommended, though I presume it could increase the sensitivity as it does for the PTT. Marlies Ledford-Kraemer provides a lucid 2004 publication on mixing studies. Thanks to Steve Duff at Precision for his reference to Marlies’ article. I’ve linked it here and hope this is helpful. Geo