A question about mixing studies from Stacy Askvig at the University of North DakotaMedical Center. Stacy’s question arrived via Lab Tests Online and the American Society for Clinical Laboratory Science Consumer Forum:
I do only PTs and PTTs, and my references seem to give me conflicting interpretations. Our patient has a prolonged PTT and DRVV, both are shortened in mixing studies:
PTT–LA 107 seconds, mix 79.5 (reference interval 0-50)
DRVV 73 seconds, mix 56.7 (reference interval 0-44)
What does this mean?
Laboratory Supervisor, Center for Family Medicine
Hello, Stacy, thanks for your question. The partial thromboplastin time (PTT) and dilute Russell viper venom time (DRVVT) are both prolonged and do not adequately correct in the mixing studies. This is presumptive evidence for the presence of a lupus anticoagulant (LA).
To confirm an LA you need to next perform a phospholipid neutralization step using a high phospholipid reagent. These are available in kit form: the PTT-based Staclot-LA kit from Stago and the LA Sure DRVVT confirmation kit from Precision BioLogic. Many hospitals send out their LA confirmation tests to reference laboratories such as Esoterix,Machaon, or Blood Center of Wisconsin. Hope this helps. Geo.