Faster determination of clottable fibrinogen in human plasma: an improved method and kinetic study

Clottable fibrinogen in human plasma was determined by measuring spectrophotometrically the increase in turbidity with time due to the fibrinogen-fibrin conversion with thrombin. From the maximal absorbance, Amax, at 450 nm obtained 2 min or less after thrombin as added to plasma, we estimated the fibrinogen concentration in plasma of normal subjects and patients. Analysis of the rate of the absorbance increase yielded the Km value, 1.6 X 10(-5) mol/liter, which closely agrees with the Km of 1.2 X 10(-5) mol/liter obtained by analysis of the fibrinopeptides released from fibrinogen.