Effects of vigorous mixing of blood vacuum tubes on laboratory test results

ObjectiveTo evaluate the effect of tubes mixing (gentle vs. vigorous) on diagnostic blood specimens collected in vacuum tube systems by venipuncture.Design and methodsBlood was collected for routine coagulation, immunochemistry and hematological testing from one hundred volunteers into six vacuum tubes: two 3.6 mL vacuum tubes containing 0.4 mL of buffered sodium citrate (9NC) 0.109 mol/L: 3.2 W/V%; two 3.5 mL vacuum tubes with clot activator and gel separator; and two 3.0 mL vacuum tubes containing 5.9 mg K2EDTA (Terumo Europe, Belgium). Immediately after the venipuncture all vacuum tubes (each of one additive type) were processed through two different procedures: i) Standard: blood specimens in K2EDTA- or sodium citrate-vacuum tubes were gently inverted five times whereas the specimens in tubes with clot activator and gel separator were gently inverted ten times, as recommended by the manufacturer; ii) Vigorous mix: all blood specimens were shaken up vigorously during 3–5 s independently of the additive type inside the tubes. The significance of the differences between samples was assessed by Student's t-test or Wilcoxon ranked-pairs test after checking for normality. The level of statistical significance was set at P < 0.05.ResultsNo significant difference (P < 0.05) was detected between the procedures for all tested parameters. Surprisingly only a visual alteration (presence of foam on the top) was shown by all the tubes mixed vigorously before centrifugation (Fig. 1 A, B and C). Moreover the serum tubes from vigorous mixing procedure shows a “blood ring” on the tube top after stopper removal (Fig. 1 D).ConclusionOur results drop out a paradigm suggesting that the incorrect primary blood tubes mixing promotes laboratory variability. We suggest that similar evaluation should be done using other brands of vacuum tubes by each laboratory manager.

Fig. 1. Three types of vacuum tubes with additive after vigorously mixing.Legend: A. Sodium citrate vacuum tube before centrifugation. B. Serum vacuum tube with clot activator and gel separator before centrifugation. C. K2EDTA vacuum tube. D. Serum vacuum tube with clot activator and gel separator after centrifugation. All tubes were purchased from Terumo (Terumo, Belgium).Figure optionsDownload as PowerPoint slideHighlights
► The CLSI/NCCLS documents strongly recommend following the manufactures datasheets
► Vacuum tubes manufacturer's datasheet have specific mix procedure for each type of active
► Two different procedures of primary blood tubes mixing were compared
► Surprisingly no difference between gently inversion and vigorous mix (shake) was recorded