Impact of low volume citrate tubes on results of first-line hemostasis testing

INTRODUCTION: Pediatric tubes are increasingly used for drawing blood for hemostasis testing. This study has investigated the potential impact of low volume citrate tubes on results of first-line hemostasis testing.

METHODS: The study population comprised 34 patients on warfarin therapy and 17 ostensibly healthy volunteers. Blood was collected into five different evacuated blood tubes from each subject. On right arm, blood was drawn directly into two standard evacuated blood tubes (3-mL Vacuette and 2-mL Vacutest) and one evacuated low volume blood tube (1-mL Vacuette) by straight needle venipuncture. On left arm, blood was drawn using a 5-mL syringe and then transferred within two nonevacuated microtubes (0.5 mL MiniCollect and 0.5 mL Micro Test). Prothrombin time (PT), activated partial thromboplastin time (APTT), and fibrinogen were assayed on ACL TOP 700.

RESULTS: Spearman's correlation of PT, APTT, and fibrinogen values obtained using different tubes was always satisfactory (ie, ≥0.93). A statistically significant bias was frequently found by comparing values obtained in different tubes. Nevertheless, the minimum quality specifications for bias were exceeded only by comparing data of Vacuette 1 mL with those of all other blood tubes for PT, by comparing data of Micro Test 0.5 mL with those of all other blood tubes for APTT, and by comparing data of Micro Test 0.5-mL blood tubes with those of Vacuette 3 mL and Vacuette 1.

CONCLUSION: First-line hemostasis testing using low volume citrate tubes may display differences sometimes exceeding the minimum quality specifications.