A New Automated Fibrinogen Assay By Using A Standard Prothrombin Time Test Procedure In An Automated Photoelectric Clot Timer

A new electronic system was developed for measuring fibrinogen in undiluted plasma during a clotting reaction. The new electronic circuit can pick up the signal coming from the photoelectric sensor of an automated coagulizer (in our case a Dual Channel of Warner Lambert Company) without interfering with its normal function. The signal produced by the clotting reaction is electronically elaborated and then sent to a four digit display which shows directly after adequate scale adjustment the concentration of fibrinogen in mg%. Electronic details of this system are patent pending. Fibrinogen electronic assay can be performed by using as reagent a tissue thromboplastin (Simplastin Automated) in the standard test procedure for prothrombin time. This system permits to obtain simultaneously in the same cuvette the determination of prothrombin time and fibrinogen. The time required for fibrinogen determination by fibrinogen electronic assay with tissue thromboplastin (FEATT) depends on prothrombin time and is about 50 sec in samples showing a prothrombin time of 30 sec. Fibrinogen can be correctly measured even in samples showing a prothrombin time as long as 100 sec. Reproducibility of FEATT showed a C.V. of 0.8 and 4% respectively at fibrinogen levels of 500 and 100 mg%. Fibrinogen concentrations as low as 10 mg% could be measured by FEATT. Heparin up to a concentration of 4 u/ml of plasma did not influence fibrinogen assay by FEATT. A good correlation was found between FEATT and methods currently used for fibrinogen assay performed on normal and abnormal samples (Parfentiev method, r=0.957; Clauss method, r=0.869; biuret assay of clottable protein, r=0.943).