Terada et al. presented an important study on the dynamic relationship between plasma fibrinogen concentration and functional clot strength after cardiopulmonary bypass (CPB).¹ Their findings underscore the multifactorial nature of coagulation monitoring in cardiac surgery requiring CPB, where numerous interacting factors influence hemostasis. The study also cautions against relying solely on a single laboratory value for clinical decision-making.

The authors suggest that hematocrit reduction after CPB explains the increased regression slope between Clauss fibrinogen and thromboelastography (TEG)-derived citrated functional fibrinogen, but hematocrit values were similar immediately compared with 1 hour after administration of protamine.¹ The regression slope in TEG also approached baseline values at 1 hour, strongly suggesting that other factors—such as factor XIII consumption, impaired thrombin generation, and accumulation of fibrinogen degradation products—likely accounted for the difference observed immediately after protamine administration.^2–4 This discrepancy between Clauss fibrinogen values and viscoelastic measurements further underscores that fibrinogen concentration alone most likely does not adequately reflect postoperative coagulative function. We demonstrated that combined assessment of fibrinogen levels and viscoelastic parameters correlates closely with postoperative bleeding risk.⁵ Taken together, these findings suggest that integrated evaluation using multiple monitoring modalities, rather than reliance on a single parameter, offers a more reliable foundation guiding transfusion management after cardiac surgery with CPB.^5,6

This study demonstrates that the relationship between Clauss fibrinogen values and viscoelastic hemostatic assays (VHAs) differs at 1 hour after CPB compared with the immediate period after administration of protamine.¹ Previous reports linking VHAs to postoperative bleeding risk have generally specified the timing of measurement,^5,7 although the timing itself varies considerably across studies. The current work emphasizes the importance of the timing of VHA measurement, as the clinical interpretation of clot strength depends not only on the measured values but also when they are determined. However, because platelet concentrates and fresh frozen plasma were administered within 1 hour in this cohort, we believe that the trajectory of the relationship between fibrinogen concentration and viscoelastic parameters remains uncertain.

In conclusion, Terada et al. provide valuable evidence that fibrinogen concentration cannot be interpreted in isolation after CPB. Their study highlights the need for combined assessment using VHAs and conventional assays, with careful attention to the timing of measurement.