Preanalytical variables and off-site blood collection: influences on the results of the prothrombin time/international normalized ratio test and implications for monitoring of oral anticoagulant therapy - van Geest-Daalderop,J.H.; Mulder,A.B.; Boonman-de Winter,L.J.; Hoekstra,M.M.; van den Besselaar,A.M. (Clin Chem, 2005)