Sometimes when I run the Chromogenix Coamatic® FVIII assay, I see an upward drift in my activity from the first to the last samples. Why is this?

Thrombin, 1 NIH unit, is included in the factor reagent. It has been shown that thrombin can activate FX, and over time you will see an increase of up to 5% activity. If you are doing numerous samples at once on an automated instrument, you might want to consider Coatest® FVIII.