Quantitative determination of fibrin and fibrinogen in biological material.

In order to measure quantitatively fibrin and fibrinogen in biological material such as thrombi, exudates, or tissues, the following method was developed and tested on model thrombi of different composition. Any fibrin and fibrinogen present is proteolytically degraded by endogenous and/or exogenous plasmin to their common late, soluble fragments D and E. Fragment E is determined by electroimmunoassay using a specific antiserum. From the amounts of fragment E the original fibrin(fibrinogen) antigen and thus of fibrin plus fibrinogen can be calculated on the basis of a molecular weight ratio of 340,000 for fibrinogen to 48,500 for fragment E. Purified fibrinogen degraded to fragments by plasmin resulted in a yield of 89.9% +/- 1.5 of the expected amount of fragment E. Fibrin under identical conditions resulted in a yield of 84.0% +/- 2.4, whereas crosslinked fibrin gave yields of 78.2% +/- 9.2 only after prolonged incubation. Control studies demonstrated that the presence of plasma proteins did not change the yield of fragment E. Measurement of the fibrin(fibrinogen) content of thrombotic material contained in surgically removed human aortic aneurysms demonstrated the validity and applicability of this method to biological material.