We sought to compare coagulation test results obtained from patients using 2 plastic blood collection tubes and the traditional glass blood collection tube. Blood specimens were obtained from 241 patients in 3.2% buffered sodium citrate using standard glass tubes, in 3.2% buffered sodium citrate in plastic tubes, and in 3.2% sodium citrate "sandwich" tubes (plastic within plastic). All samples were obtained and processed contemporaneously and tested for prothrombin time (PT) and activated partial thromboplastin time (aPTT). Residual plasma was frozen at -70 degrees C for future testing, including fibrinogen, antithrombin, plasminogen, protein C and protein S (functional and antigenic), dilute Russell viper venom time (DRVVT), ristocetin cofactor, factor XIII, D dimer, anti-Xa activity, and prothrombin fragment. Although paired t test analysis revealed statistically significant differences (P < .05) between glass and plastic for PT, aPTT, fibrinogen, protein C (functional and antigenic), functional protein S, DRVVT and confirmation method, antithrombin, and factor XIII, these differences were not considered clinically significant.