High haematocrit in cyanotic congenital heart disease affects how fibrinogen activity is determined by rotational thromboelastometry

IntroductionViscoelastometry enables rapid evaluation of coagulopathy in settings such as cardiac surgery but may be influenced by red cell concentration.MethodsIn order to study the effects of supra-physiological red cell concentrations on viscoelastometry, we compared ROTEM® viscoelastometry and plasma coagulation assay results in high haematocrit (HCT; 0.55-0.76 L/L) blood from patients with cyanotic congenital heart disease (CCHD), and in model high HCT blood (HCT 0.45-0.70 L/L).ResultsHigh HCT blood from CCHD patients (median HCT 0.66 L/L) displayed prolonged clot initiation in the EXTEM® test compared to controls and reduced maximum clot firmness (MCF) in the EXTEM (median 51 mm vs 64 mm in controls) and FIBTEM® (7 mm vs 14 mm) tests. The plasma fibrinogen (Clauss; CF) was similar in CCHD blood to controls (median 2.94 g/L vs 2.49) but the whole blood fibrinogen concentration (WBFC) was reduced (1.27 g/L vs 1.58). The FIBTEM MCF correlated linearly with the CF (r2 = 0.68; p < 0.0001) and WBFC (r2 = 0.65; p < 0.0001) in control blood but this relationship was maintained only with WBFC in CCHD blood. Model high HCT blood showed abnormal ROTEM test results that were similar to CCHD blood, including reduced FIBTEM MCF (14 mm with HCT 0.32-0.44 vs 6 mm with HCT 0.63-0.70). The ROTEM results were HCT dependent but independent of plasma clotting times and fibrinogen concentration.ConclusionSupra-physiologic HCT causes abnormal ROTEM test results consistent with increased dilution of fibrinogen and coagulation factors in whole blood by red cells. High HCT should be considered during interpretation of ROTEM test results in clinical settings.