Determination of heparin in the blood

A method of determining the concentration of heparin in blood in heparinized patients, comprising the steps of equilibrating normal human plasma at a selected temperature, adding serum from said blood to standardized thrombin solution and incubating the resultant thrombin-serum mixture at said selected temperature and for a selected period, said period at said selected temperature being such as to be too brief for substantial reaction between said thrombin and any fibrin degradation products in said serum while sufficient for reaction of heparin with said thrombin, adding a standard portion of said incubated thrombin-serum mixture to said plasma under conditions such as to produce an essentially uniform thrombin-serum-plasma mixture, observing the clotting time thereof, said clotting time being an inverse function of the quantity of thrombin remaining after reaction with said heparin and thereby a direct function of the concentration of heparin in said blood, and comparing the thus-determined clotting time with a curve prepared by adding different quantities of heparin to serum specimens taken from healthy individuals to form heparin-serum solutions, adding each heparin-serum solution to thrombin solution and incubating for said selected period at said selected temperature, adding the incubated heparin-serum-thrombin solution to normal plasma incubated at said selected temperature and noting the clotting time, thereby determining clotting times as a function of heparin content of serum, thus making it possible to specify the heparin content of a patient's blood by measuring the clotting time of serum taken from the blood of said patient.