Validation of a point-of-care prothrombin time test after cardiopulmonary bypass in cardiac surgery

Point-of-care coagulation monitoring can be used for the guidance of haemostasis management. However, the influence of time on point-of-care prothrombin time testing following protamine administration after cardiopulmonary bypass has not been investigated. Bland-Altman and error grid analysis were used to analyse the level of agreement between prothrombin time measurements from point-of-care and laboratory tests before cardiopulmonary bypass, and then 3 min, 6 min and 10 min after protamine administration. Prothrombin times were expressed as International Normalised Ratios. While the point-of-care and laboratory prothrombin time measurements showed a high level of agreement before bypass, this agreement deteriorated following protamine administration to a mean (SD) bias of -0.22 (0.13) [limits of agreement 0.48-0.04]. Error grid analysis revealed that 35 (70%) of the paired values showed a clinically relevant discrepancy in international normalised ratio. At 3 min, 6 min and 10 min after cardiopulmonary bypass there is a clinical unacceptable discrepancy between the point-of-care and laboratory measurement of prothrombin time.