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Background During cardiac surgery with heart-lung-machine support, abdominal swabs are routinely used to adsorb blood from the operation field. In part, abdominal swabs exhibit procoagulant activity, which is usually considered harmless. However, coagulation induction and abnormal clot formation on the surface of abdominal swabs in the operation field may, if the blood is retransfused into the extracorporeal circuit, lead to severe thromboembolic complications. The aim of the present study was to elucidate the origin of the unexpected blood clotting upon contact with hypercoagulant swabs. Methods The coagulant properties of three abdominal swabs were characterized using a simple clotting test and human whole blood, which was anticoagulated with different heparin concentrations. Eluates prepared from the abdominal swabs and the color stabilizer polydiallyamine (PDAA) were incubated with blood and blood clotting was investigated. Furthermore, the effects of the abdominal swabs on blood clotting time and on heparin were investigated. Results Our data show that the three abdominal swabs as well as the respective eluates exhibit distinctive coagulant properties. The abdominal swab with the highest hypercoagulant effect significantly reduced blood clotting time and also led to a reduction in free heparin. PDAA does not induce activation of the coagulation system. Conclusion The data indicate that the hypercoagulant swab reduces the clotting time and the concentration of free heparin. Abdominal swabs used during complex cardiac surgery with heart-lung-machine support should definitely be tested for their coagulant properties using appropriate tests before clinical applications, as it cannot be specified what leads to their hypercoagulant property.

During surgical procedures, abdominal swabs are routinely used to adsorb blood from the operation field and for the retention of tissues and organs. Due to the material characteristics, abdominal swabs exhibit a slight procoagulant activity, which is usually desirable and mostly harmless. However, during cardiac surgery with heart–lung machine (HLM) support, abnormal clot formation may result in life-threatening thromboembolic complications. Therefore, a simple clotting test (SCT) allowing in vitro detection of abdominal swabs with elevated hypercoagulant potency in the presence of heparinized human blood was developed and validated. In order to establish a SCT, heparinized human blood from 100 donors was incubated with five different cotton abdominal swabs for 30 min at 37 °C and then macroscopically analyzed. In a second study, 10 other swabs were screened with the established SCT (n = 11) to confirm its suitability. Scanning electron microscopy, measurements of activated clotting times and thrombin-antithrombin were further performed. In the SCT, the results are dichotomized as negative (no detectable blood clot) and positive (blood clot formation). In the first study, three of the five tested abdominal swabs exhibited hypercoagulant potency in at least 25 % of the donors. Calculations using the binomial distribution showed that blood of 11 donors is needed for routine testing with the SCT, which was confirmed in the second study using another 10 swabs. The established SCT can be used for detection of abdominal swabs with an elevated procoagulant potency, thereby minimizing the risk of thromboembolic complications during cardiac surgery with HLM support. Graphical Abstract