Summary
The most commonly used fibrinogen assays in the clinic are clotting rate assays, e.g.
the Clauss method. Such functional assays may be disturbed by e.g. heparin, anticoagulant
fibrinogen degradation products (FgDP) and in the case of a dysfi-brinogenemia. Immunological
methods would not suffer from these interferences. However, immunological assays for
fibrinogen, which do not measure FgDPs, do not exist.
To set up such an enzyme immunoassay (EIA) we developed two monoclonal antibodies.
The first monoclonal antibody (G8) has its epitope in the carboxyl-terminal 150 amino
acid stretches of the fibrinogen Aa-chains. G8 is used to coat the wells of microtitration
plates, and is the capture antibody in this EIA. The second antibody (Y18) has been
described by us previously (Blood 1985; 66: 503). It is directed against fibrinopeptide
A, covalently bound to the ±-chains i.e. against the amino-terminal stretches of the
A±-chains. Y18 is conjugated with horse-radish peroxidase, and used as tagging antibody.
The EIA does not react with, and is not interfered by FgDP such as purified fragments
X and Y, up to a concentration of 800 μg/ml. An FgDP mixture such as generated by
Streptokinase treatment of plasma does not respond. Fibrin degradation products (whole
blood lysate) up to 800 μg/ml do not interfere nor do heparin, EDTA or oxalate. The
time-to-result of the EIA is only 45 minutes. Some patient plasmas yielded dose-response
curves which are not parallel with the calibration curve of the EIA. An explanation
for this phenomenon could not be given. Our fibrinogen EIA may be especially suitable
to monitor patients with conditions which favour proteolytic damage to fibrinogen
such as thrombolytic therapies.
keywords
Enzyme immunoassay - Fibrinogen - Monoclonal antibodies
