Studies on fibrinolysin using a clinically practical method of quantitative determination.

Methods of quantitative measurement of fibrinolysin are available (Astrup and Alkjaersig, 1952; Loomis, George, and Ryder, 1947; Shulman and Tagnon, 1950). For the most part, these are fairly complicated techniques suitable for the research laboratory but not for the routine clinical laboratory. The method most generally used in the clinical laboratory is a simple qualitative technique in which the blood clot is incubated overnight at 370 C. However, this method may give false positive results in patients with fibrinogenopenia as seen, for example, in post-partum cases (Weiner, Reid, and Roby, 1950). Fibrinogenopenia has at times been misdiagnosed as fibrinolysin because of this error. The qualitative fibrinolysin test will also give false negative results when the enzyme is present in excess but is not strong enough to cause complete lysis of the clot. In these cases, Macfarlane (1937) has recommended using dilute plasma to bring out the fibrinolytic activity. While this method is an improvement over the blood-clot incubation technique, it may still give false positive and false negative results. Furthermore, it gives only a qualitative measure of the defect. Bidwell (1953) and Bidwell and Macfarlane (1951) have attempted to convert Macfarlane's qualitative technique to a quantitative one, and the method now presented is essentially a modification of this method. The quantitative method to be described is useful for any clinical laboratory that is able to do fibrinogen determinations. It has been applied to the routine investigation of coagulation problems, and in addition has been used to study the characteristics of the fibrinolysin in the plasma of a patient with carcinoma of the prostate.