The present invention is a method of extracting infectious pathogens from a volume of blood including the steps of creating a fibrin aggregate confining the pathogens and introducing a fibrin lysis reagent to expose the pathogens for analysis. The fibrin lysis reagent is preferably composed of plasminogen and streptokinase frozen in coincident relation until the fibrin lysis reagent is needed whereby streptokinase enzymatically reacts with plasminogen to form plasmin upon thawing. The plasminogen is suspended in an aqueous salt solution prior to freezing including NaCl and Na3PO4.