Coagulation tests are influenced by pre-analytic conditions such as blood collection systems. Change of glass collection tubes with plastic ones will cause alteration of the test results. The aim of this study was to compare three plastic blood collection tubes with a standard glass blood collection tube and each plastic collection tube with the other two for possible additional tube-to- tube differences.A total of 284 blood samples were obtained from 42 patients receiving warfarin during their routine controls, besides 29 healthy volunteers. Subgroup analyses were done according to health status.Our study demonstrated that different blood collection tubes have a statistically significant influence on coagulation tests. The magnitude of the effect depends on the tube used. However most of the tests performed on samples obtained from any tube correlated significantly with results obtained from other tube samples.Although blood collection tubes with different brands or properties will have distinct effects on coagulation tests, the influence of these blood collection tubes may be relatively small to interfere with decision-making on dose prescription, therefore lack clinical importance. Correlations between the results showed that, one of these plastic blood collection tubes tested in our study, can be used interchangably for a wide variety of coagulation assays.None declared.