Filling accuracy and imprecision of commercial evacuated sodium citrate coagulation tubes

Current recommendations advocate that blood tubes for coagulation testing should be filled not less than 90% of their nominal filling volume, since under- or over-filling >10% may generate unreliable results of some hemostasis assays. This study was hence aimed to explore filling accuracy and precision of commercial blood tubes. Between-lot variations of 3 different lots (20 tubes per lot) of 3.2% citrate blood tubes manufactured by Becton Dickinson, Greiner and Kima were studied. One additional lot from each manufacturer was assessed in triplicate (three series of 20 tubes), to assess within-lot variation. All tubes were first weighed empty and then filled with distilled water by a syringe, under ideal filling conditions. Filled tubes were weighed again, in duplicate. For each 20 tubes series, mean bias (deviation from the ideal tube filling volume) and imprecision (coefficient of variation; CV%) were calculated. All biases were within ±10%. Within-lot and between-lot variation in filling volume was acceptable, and comprised between 0.4 and 2.4%. Greiner tubes were the most accurate (bias, -1.0 to 2.4%), followed by Kima (bias, -7.8 to -5.9%) and Becton Dickinson (bias, -9.6 to 3.3%) tubes. The highest between-lot difference was noted for Becton Dickinson tubes (up to 12.9%), followed by Greiner and Kima tubes (up to 3.4 and 1.8%, respectively). Although coagulation tubes filling accuracy was within ±10% for all three tested manufacturers, the overall bias was found to be variable among manufacturers and lots. Major effort shall be made by blood tube manufacturers for improving standardization of their products.