From Monali Gupta MD, Toronto General Hospital:
Hi George, I compliment you for creating such a wonderful website to understand and learn coagulation. The modules are very educative. I have two questions about the DTI assay described in Module 28, Thrombin Time Assay.
- Why patients’s plasma is diluted in 1:8 or 1:20 in saline?
- Why pipetting has to be done forcibly for human TT reagent?
Also, I faced a problem in listening to slides 17–19 as these slides show buffering and don ot play. Thanks for creating such a wonderful learning portal.
Hello, Dr. Gupta, and thank you for your kind words. I couldn’t reproduce the problem for slides 17–19 on my Mac, but I have forwarded your message to our technical support group for possible updates. By the way, the International Society on Thrombosis and Hemostasis bieenial meeting begins on Saturday in Toronto, perhaps we will have the opportunity to meet there.
The patient plasma dilution has been determined empirically by the kit manufacturer so that the results of the assay fall within the linear range. Dilutions are specific to the antthrombotics being measured, agatroban, bivalirudin, or dabigatran (lepirudin is no longer available). Most thrombin time testing is performed on automated or semiautomated analyzers, so pipetting technique is no longer a specific concern for the laboratory scientist. However, when performing a manual TT, PT, or PTT, the final reagent is pipetted forcibly as the timer begins in an effort to have a clear starting point. Pipetting slowly would lengthen the clot initiation phase. I hope this helps, and I again thank you for your question.