Abstract: A one-stage prothrombin assay which measures the exponential rate of thrombin production in thromboplastin-treated, recalcified plasma. A serum reagent reduces the lag time before thrombin production substantially to zero for both normal and abnormal plasma, thus allowing measurements to be made in just a few minutes.

Abstract: A quantitative method and composition for precipitating fibrin monomers from plasma in the presence of fibrinogen, with only a small amount, if any, of fibrinogen being precipitated. A buffered precipitating agent is provided having a pH in the range of 6.5.+-.0.5, the buffer being one having a pKa in the range of 6 to 7 and protamine sulfate at a level of 0.025 to 0.2% by weight. Suitable buffers are 2-(N-morpholino)ethanesulfonic acid, sodium phosphate, histidine, maleic acid and imidazole. Analysis of the amount of fibrin present can be made by analyzing for protein using preferably a basic urea solution containing sodium hydroxide and measuring the absorbance at 282 nanometers.