[Fibrinogen as a source of interference in heterogeneous enzyme immunoassays]

Fibrinogen interferes in heterogeneous enzyme immunological in vitro tests. The effect on the test result is variable and depends on the test principle (competitive binding analysis or sandwich technique). In the tests for digoxin, cortisol, alpha 1-fetoprotein and acid prostate phosphatase, the use of plasma as sample material resulted in varying degrees of interference. In the case of the digoxin determination, using the Enzymun-Test Digoxin, it is possible to abolish interference by fibrinogen by thermal coagulation (plasma is heated at 56 degrees C for 30 min) and removal of the fibrinogen. Alternatively, addition of urea to the antigen-antibody reaction mixture decreases the interference caused by fibrinogen. The added quantity of urea and the time of incubation must be optimized for each sample material.