Over the past several years, the use of plastic specimen tubes throughout the laboratory has been on the rise for several reasons, including lower risk of breakage, which reduces biohazard exposure risk, and lighter weight, which reduces shipping and disposal expenses. Regulatory agencies have also strongly encouraged the use of plastic tubes and tube manufacturers have discontinued the production of many types of glass tubes.

Coagulation testing is known to be sensitive to the composition of specimen tubes [9], and historically, coagulation specimens have been collected in siliconized glass tubes to limit contact activation of clotting factors. Several studies comparing coagulation test results on plastic versus glass tubes found statistically significant differences in PT results between tube types, but in most cases the differences were deemed to be clinically insignificant [10, 11]; however, the differences were deemed potentially clinically significant in two studies [8, 12]. Rodgers and colleagues evaluated the effect of plastic tubes on esoteric coagulation tests, including factor assays, thrombin time, lupus anticoagulant, von Willebrand factor, protein C, protein S, APC resistance, and antithrombin, with normal donor plasma specimens. They found that the only test significantly affected was the thrombin time [13].

CLSI considers either glass or plastic tubes to be acceptable, provided that the inside surface is non-activating [1]. Nevertheless, before changing from one tube type to another, it is advisable for laboratories to evaluate the effects, if any, on their coagulation assays by conducting crossover studies using specimens with normal and abnormal results.

Several options are available for collecting blood specimens for coagulation testing, including venipuncture blood collection systems into evacuated tubes, winged needles and tubing, syringes, vascular access devices (VADs), and capillary specimens. Of these, the recommended method is venipuncture collection directly into tubes containing anticoagulant [1]. The other methods all have potential problems that may affect specimen quality. Winged collection systems have a length of tubing whose dead-space may result in under-filled tubes or activation of clotting factors or platelets if not properly managed. Syringe draws may result in activation of clotting factors when there is a delay in transferring blood from the syringe to the anticoagulated specimen tube. Syringe draws may also cause hemolysis if blood is drawn into or expelled from the syringe with too much force. VADs may lead to heparin contamination if the line is heparin-imbedded, has been flushed with heparin, or has had heparin administered through it. VADs may also lead to specimen dilution or partially clotted blood if the dead space is not managed appropriately. Capillary specimens are subject to activation of clotting factors if blood is not flowing freely, dilution with extracellular fluid if the skin puncture site is squeezed too vigorously, and hemolysis if the puncture site is overly “milked.”