Freeze-dried activated substrate for factor VIII assays

Factor VIII-deficient plasma (natural or artificial) mixed with kaolin and phospholipid can be lyophilized to provide ready-to-use substrate which is stable for months at 4 degrees C and usable after many weeks at room temperature. Factor VIII assays are much simplified and more reproducible using this reagent and can be quantified with the aid of a programmable calculator according to the equation (formula; see text) as % of standard and X, S and B are clotting times of test, standard and blank samples respectively. The slope of the log/log function (k) is approximately--6.5.