From Dr. Mirta Arias: Dear George, Thank you for your answer in the blog. I have another question. Dr. Robinson in ISLH argued that it is good to chill the post 2 hour/37°C 37 incubation mixtures of patient + pool normal plasma, and control at 2–8°C for 10 minutes and then measure the factor VIII. In this way, the inhibitor stops reacting and you can generate more accurate results. What do you think about this?
Hello, Dr. Arias, and thank you for your question. I referred it to Dr. Connie Miller and Ms. Amanda Payne of the US Centers for Disease Control and Prevention, with this comment: It seems like the inhibitor’s anti-factor VIII activity is stabilized within the two-hour incubation so that nothing could be accomplished by chilling. Also, after chilling for 10″, one would have to let the tubes stand a few minutes to return to ambient before testing. What is your opinion?
Here is Dr. Miller’s response: Hi George, I understand the rationale for chilling the specimen after incubation, and such a step might be useful if a delay were necessary between removing the specimens from incubation and measuring the FVIII:C. Such a delay, however, is not recommended; measurement should take place immediately. There is no evidence that I am aware of that the rate of the reaction will significantly alter the results in the minimal time that it usually takes to transfer the specimens or that chilling would immediately stop it. If one is consistent in the time from incubation to measurement, I do not believe that it is necessary to add a chilling and re-warming process to an already lengthy assay. Regards, Connie.