Level of Agreement between Laboratory and Point-of-Care Prothrombin Time before and after Cardiopulmonary Bypass in Cardiac Surgery

BACKGROUND:

Hemostasis monitoring in cardiac surgery could benefit from an easy to use and fast point-of-care coagulation monitor, since routine laboratory tests have a delay of 30-45minutes. This study investigated the level of agreement between the point-of-care prothrombin time (PT) with central laboratory PT before and after cardiopulmonary bypass.

METHODS:

Bland Altman and error grid analysis were used to analyze the agreement between the point-of-care Coaguchek XS Pro device (POC-PT) and the central laboratory prothrombin time (LAB-PT) before cardiopulmonary bypass (CPB) and 3minutes after protamine administration. Prothrombin times were expressed in international normalized ratios (INR).

RESULTS:

The average POC-PT and LAB-PT values of 73 patients were 1.06±0.14 and 1.09±0.13 (P=0.10) before CPB. POC-PT measurements before CPB showed a good agreement with the LAB-PT, with a bias of -0.02±0.07 INR and 94% of the values being represented in the clinical acceptable zone of error grid analysis. The mean POC-PT 3minutes after protamine administration was significantly lower than the LAB-PT (1.35±0.12 vs. 1.70±0.18; P<0.001). The PT at 3minutes after protamine administration showed a bias of 0.36±0.14, and 82% of the values were located outside of the clinical acceptable zone in the error grid analysis.

CONCLUSIONS:

Point-of-care prothrombin time testing was in concordance with conventional laboratory PT prior to cardiopulmonary bypass. At 3minutes following protamine administration, PT values of the point-of-care device were structurally lower than the laboratory PT values, leading to a disagreement between both tests at that time point.