Latex Immunoturbidimetric Assay for Soluble Fibrin Complex

Background: Soluble fibrin complex (SFC), composed of fibrin monomer and fibrinogen derivatives, is known to exist in the circulating blood in patients with thrombosis. Its detection and quantification are useful for obtaining information about the condition and degree of intravascular coagulation in early-stage thrombosis, but there is no rapid method to measure SFC in plasma for clinical use. Methods: We obtained a monoclonal antibody that specifically reacts with SFC, with desAA-fibrin as the immunogen, and developed a rapid and sensitive latex immunoturbidimetric assay (LIA) using latex-immobilized anti-SFC monoclonal antibody. The assay system was based on the increase in turbidity induced by the reaction of the latex-immobilized anti-SFC monoclonal antibody with SFC in plasma, and the assay procedure was fully automated on a Hitachi 911 analyzer. Results: The method had an analytical range of 3–300 mg/L. Intra- and interassay precision studies indicated that this system provided reproducible data (CVs <3.0% and <2.0%, respectively). The assay detection limit was <0.5 mg/L. There was no interference from bilirubin (up to 440 mg/L), hemoglobin (up to 9.6 g/L), Intralipid (up to 10%), D-dimer (up to 200 mg/L), and rheumatoid factor (up to 470 000 IU/L). SFC concentrations in plasma from patients with thrombotic diseases [mean (SD), 48.9 (57.6) mg/L; n = 160) were significantly higher than those in plasma from healthy individuals [1.8 (2.1) mg/L; P <0.001; n = 304]. Conclusion: In terms of linearity, precision, and sensitivity, the LIA, performed on a Hitachi 911 automated analyzer, may be useful for measurement of SFC in plasma.