All of these kits measure the same thing — factor VIII activity in plasma and potency estimation of FVIII concentrates. Coamatic FVIII includes the FXa substrate S-2765, and the factor reagent FIXa + FX and thrombin colyophilized with CaCl2 and phospholipid. The Coatest SP FVIII includes the FXa substrate S-2765, and the FIXa + FX reagent, CaCl2, and phospholipid are all separate components in the kit. Incubation times are a little longer, and the reagent prep is less simple. Coatest SP4 FVIII is exactly the same as Coatest SP FVIII, but the FIXa + FX reagent is divided into 4 vials of 1.8 U (reconstituted with 3 ml) instead of 1 vial of 6 U (reconstituted with 10 ml).