From “Ipaz” at Iline Microsystems: For the plasma dilute thrombin time, why is the patient plasma diluted with normal pool plasma and not with saline solution?
Thank you for your question. The dilute thrombin time is currently produced by Hyphen BioMed and marketed in North American by Aniara as their Direct Thrombin Inhibitors assay. The assay is designed to monitor the efficacy of dabigatran, hirudin, and argatroban, and is labeled for research use only in the USA. Patient plasma containing a direct thrombin inhibitor (DTI) is first diluted (1:8 for dabigatran) using phosphate buffered normal saline or Owren-Koller buffer. Next, pooled normal plasma is added, then purified human α-thrombin, and the interval to clotting is recorded and compared to DTI calibrators.
Diluting the patient plasma and adding back normal plasma enhances assay reproducibility. The patient’s DTI acts upon a predictable level of thrombin provided in the normal plasma, and variations in patient procoagulant activity have little effect upon the clotting time. Hyphen claims a linear response to DTIs within their therapeutic intervals, and inter-assay CV%’s of < 5%. I suspect that as the use of dabigatran grows and its bleeding risks are documented, we will be asked to perform more and more dilute thrombin time assays.
In follow-up (later the same day), Jonas Kingo of Aniara contacted Dr. Jean Amiral, President and Scientific Director of Hyphen BioMed: Here is Jonas’ and Dr. Amiral’s response: Hello George, here is the answer from Dr. Amiral:
Dear Jonas, A plasma pool is used for diluting the tested plasma for thrombin Inhibitors in order to allow clotting, and to render the assay insensitive to variable coagulation factors in tested specimen (mainly II and Fbg). Best regards, Jean