FXII decline during cardiopulmonary bypass and the limits of routine coagulation assays: a prospective observational analysis

BACKGROUND: The contact activation system is triggered when blood comes into contact with artificial surfaces. Cardiopulmonary bypass (CPB) induces such activation, however the extent of factor XII (FXII) reduction and its reflection in routine coagulation assays remain unclear. METHODS: In this prospective observational study, 20 adult patients undergoing elective cardiac surgery with CPB (10 coronary artery bypass grafting (CABG), 10 aortic aneurysm repair) were analyzed. Blood samples were collected immediately prior to anesthesia induction (T1) and three minutes after protamine administration (T2). Laboratory analyses included FXII, factor VIII (FVIII), and factor V (FV) activities, activated partial thromboplastin time (aPTT), prothrombin time (Quick/INR), fibrinogen, and viscoelastic testing (ROTEM). RESULTS: FXII activity decreased significantly after CPB (whole cohort: 98% (79/122) vs. 62% (51/83); CABG: 108% (83/124) vs. 64% (47/85); aortic: 92% (75/119) vs. 61% (52/82), p < 0.001 each). FV declined, whereas FVIII tended to increase. aPTT prolongation was minimal and remained within the normal range. A strong correlation between FXII decline and aPTT change was observed only in CABG patients (ρ = - 0.835, p = 0.003). ROTEM clotting times were moderately prolonged after CPB but showed no correlation with FXII activity. CONCLUSIONS: CPB induced a significant reduction in FXII activity. Global coagulation assays such as aPTT or ROTEM have limited sensitivity for contact factor deficiencies. Isolated prolongation of these parameters after CPB should be interpreted cautiously and, in the absence of clinical bleeding, should not routinely prompt hemostatic interventions. Future studies should address subgroup differences (CABG vs. aortic surgery) in larger cohorts. TRIAL REGISTRATION: The trial was registered in the German Clinical Trials Register (DRKS00034174).