[Comparison of Quick/INR values of whole capillary blood (CoaguChek Plus) and venous citrate plasma in patients with and without oral anticoagulation].

Background: The prothrombin time, also called thromboplastin time ("Quick"), is usually measured by using citrated plasma from venous blood. Recently, portable coagulation monitors have been developed which measure prothrombin time using non-anticoagulated capillary whole blood from a finger-stick. In the present study we evaluated the CoaguChek Plus coagulation monitor in comparison with a standard laboratory method in various patient groups: patients on oral anticoagulation with or without heparinisation, patients receiving heparin without oral anticoagulation, patients with a deficiency of one of the coagulation factors of the extrinsic or common pathway, and patients with liver disease. Furthermore, we studied the influence of the haemoglobin concentration on the test results.
Method: Capillary prothrombin time was measured by using the portable coagulation monitor CoaguChek Plus and venous prothrombin time was assessed by using Thromborel S.
Results: We found a correlation coefficient of 0.94 between capillary and venous INR values in 216 determinations from 167 patients. The slope of the regression line was 1.03, and the y-intercept 0.05, 93.5% of the results were within 0.9, 90.7% within 0.7, and 83.8% within 0.5 INR units. Similar results were obtained in patients on oral anticoagulation, patients with a deficiency of a factor of the extrinsic system and in patients with liver disease. Correlation and agreement were somewhat lower among patients on oral anticoagulation and simultaneous heparinisation (40 patients): correlation coefficient was 0.83, slope of the regression line was 0.87 and y-intercept was 0.27 INR units. No influence of the haemoglobin concentration on INR results could be demonstrated.
Conclusion: Our results show the CoaguChek Plus coagulation monitor to be a valuable tool for measuring prothrombin time in patients on oral anticoagulation, in patients with liver disease to estimate the capacity of protein synthesis, and to screen for possible deficiencies of one of the coagulation factors of the extrinsic or common pathway. However, based on our preliminary data we cannot recommend the use of the CoaguChek Plus coagulation monitor in heparinised patients.