This is from Ann McConnell, East Carolina University, first posted on November 19: Why are factor activity assays reported in the range of 50%–150%? I am having a difficult time wrapping my mind around the concept that something can be more than 100% “active.” Thanks!
Hello, Dr. McConnell, and thank you for your question. To be honest, the correct way to express coagulation factor activity is in international units, with 1 IU = the mean factor activity of normal plasma. Thus 150% would be 1.5 units. From a pure mathematical standpoint, percent is an incorrect expression, however, we’ve been using it to express factor activity since the mists of time, so, given normal human inertia, we probably won’t change!
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