ABSTRACTPlatelet Mapping can measure both the degree of platelet inhibition and fibrinogen activation, was not originally designed to measure fibrinogen concentration. Traditional laboratory fibrinogen concentration testing requires around 60 minutes; however, fibrinogen activation only takes 10 minutes, and is indicated as maximum amplitude of activator f. If Platelet Mapping can predict fibrinogen concentration during cardiopulmonary bypass, this could facilitate rapid hemostasis management. The aim of this study was to verify whether fibrinogen concentration could be predicted using Platelet Mapping results. Thus, a pilot study was conducted to evaluate this concept during cardiopulmonary bypass. This prospective, observational pilot study investigated 15- to 90-year-old patients who underwent cardiac or aortic surgery from August 2019 to September 2019. Twenty-one patients enrolled in this study, and 43 blood samples were obtained for both fibrinogen activation measurements using Platelet Mapping and traditional laboratory-based tests, respectively. Correlations between results were analyzed using linear regression and the receiver operating characteristic curve. Correlation by Pearson’s correlation analysis indicates a significant relationship (correlation coefficient of r = 0.91), and a receiver operating characteristic curve indicated that sensitivity, specificity, and receiver operating characteristic area were 100% (95% confidence interval, 75.3–100%), 93.8% (79.2–99.2%), and 0.995 (0.984–1.00), respectively. Our results indicate a strong correlation between fibrinogen activation and serum fibrinogen concentration. The maximum amplitude of activator f can estimate low fibrinogen concentration faster than traditional methods; this method quickly provides important information for anesthesia and hemostatic management in cardiac surgery.