An Evaluation of Technics for the Separation and Estimation of Plasma Fibrinogen.

A proposed heat precipitation and thrombin interaction technic for fibrinogen isolation has been compared with a sulfite fractionation technic. All three methods exhibit a high degree of correlation. Fibrinogen, which has been separated from plasma by these technics, may be quantitated by the colorimetric modified biuret and phenol-biuret reaction. For direct measurement of fibrinogen, heat precipitation followed by ultraviolet spectrophotometry appears to be the technic of choice. The method of measurement at two different wave lengths does not appear to present any advantage over single wave length measurement at 240 and 220 mJL. Free hemoglobin in concentrations below 800 mg./h00 ml. of plasma does not interfere with the sulfite fractionation technic but seriously interferes with the ultraviolet measurements in concentrations above 200 mg./100 ml. Bilirubin interferes with sulfite fractionation in concentrations above 24 mg./100 ml. but not with the heat precipitation technic for fibrinogen estimation. Lipids in excess above normal amounts interfere with both the sulfite fractionation and heat precipitation technics. Normal values for plasma fibrinogen from a variable age group using the sulfite fractionation technic and modified biuret end point have been determined.