A comparative study of new generation blood sampling tubes for thrombophilia investigations

Abstract number: P1041

Smith^* J. M., Bowyer^* A. E., Cooper^* P. C., Pastorelli^* D., Makris† M., Kitchen^* S.

^*Royal Hallamshire Hospital, UK; †University of Sheffield, UK

For many years, laboratories have used BD Vacutainer siliconised glass blood collection tubes containing 0.105 M buffered sodium citrate for thrombophilia tests. We have investigated two new generation BD Vacutainer tubes: Plus Citrate, a plastic tube containing buffered 0.109 M citrate, and siliconised glass CTAD tubes, which contain 0.109 M buffered citrate with theophylline, adenosine and dipyridamole (CTAD). Chromogenic assays of antithrombin (AT) (Dade Behring) and protein C (PC) (using Protac and S2366) and anticoagulant assays of protein S (PS) (Helena BioSciences Europe) and factor V-corrected APC-Resistance tests (APCR-V) (Chromogenix) were performed on a Sysmex CA6000 analyzer. The protein C assay included a blank (PC-Blank) as the assay is sensitive to contact factor activation. Samples were collected into each tube in randomized order, from 30 normal and 30 individuals with a previously diagnosed thrombophilic tendency, centrifuged twice at 2000 × g and the plasma stored at -70 °C prior to testing. Comparing Glass-Citrate, CTAD and Plus-Citrate tubes the following means were calculated, respectively: AT 1.01, 1.02, and 0.99 IU mL^-1; PC 0.84, 0.86 and 0.83 IU mL^-1; PS 0.87, 0.89 and 0.88 IU mL^-1; APCR-V 2.40, 2.40 and 2.41. Using multivariate analysis statistically significant differences were seen in the mean values for AT between Glass-Citrate vs. Plus-Citrate (P < 0.05) and Plus-Citrate vs. CTAD (P < 0.001), and for PC between Glass-Citrate vs. CTAD (P < 0.01) and Plus-Citrate vs. CTAD (P < 0.001), however, these differences are small and would not influence clinical management. No statistically significant differences were seen between the mean values for APCR-V and PS when comparing any of the tube systems. PC-Blank optical densities were less than 0.006, with a median value of 0.001 for all tubes, showing no statistically significant difference between tube types (P > 0.05).We conclude therefore that both new generation tubes are suitable alternatives to Glass-Citrate for thrombophilia screening, using the methods applied in this study. Tube specific normal ranges are recommended for antithrombin and protein C activity.