Method Description

Coagulometric (turbidimetric) detection is based on the principle that light passing through a medium in which fibrinogen is converted to fibrin is absorbed by the fibrin strands. Light at 671 nm is transmitted through a sample onto a photodetector, which is positioned 180 degrees to the source. Light absorption increases as fibrin clot formation progresses. Consequently, light transmittance through the sample continuously decreases and is measured by the photodetector. The corresponding electrical signal output from the photodetector changes according to the detected light. The signal output is processed via software through a series of algorithms to determine the clot point.

In 1957, Clauss developed a quantitative assay using thrombin to measure fibrinogen in plasma. In this procedure, an excess of thrombin is added to diluted plasma, and the resulting clotting time value is measured. The log of the clotting time value is inversely proportional to the log of the fibrinogen concentration. A fibrinogen reference curve is plotted from the clotting time results of the known reference plasma dilutions having different fibrinogen values. The concentration of fibrinogen in patient plasma samples is determined by comparing clotting time values to the reference curve.(Package insert: HemosIL Q.F.A. Thrombin [Bovine]. Instrumentation Laboratory; R10, 06/2017; instruction manual: IL TOP Operators Manual, Instrumentation Laboratory; 2013)