Processing of diagnostic blood specimens: is it really necessary to mix primary blood tubes after collection with evacuated tube system?

Background: The preanalytical phase is considered the most vulnerable phase in biopreservation, biobanking, and laboratory diagnostics. Accurate mixing after blood collection is claimed to be important and recommended by the manufacturers.

Objective: To evaluate whether it is really necessary to mix the primary blood tubes immediately after blood collection by means of evacuated tube systems.

Material And Methods: Blood from 300 outpatients was equally and randomly divided into three groups: G1, sodium citrate vacuum tubes; G2, lithium heparin vacuum tubes; and G3, K2EDTA vacuum tubes. All vacuum tubes were processed using three different procedures. Procedure 1: Gold Standard (P1): All specimens mixed gently and carefully by inverting five times as recommended; Procedure 2: Rest time (P2): All specimens remained 5 min in the upright position, followed by gentle careful mixing by inverting five times; Procedure 3: No mix (P3): All specimens were left in upright position without mixing afterwards. The influence of the primary mixing tube procedure was evaluated for clinical chemistry, hematology, and coagulation parameters by paired t-test. The bias from the mixing procedure was also compared with quality specifications derived from biological variation.

Results: Significant differences (p<0.017) were found for: i) red blood cell count and hematocrit when P1 was compared with P2; ii) alanine aminotransferase and erythrocyte sedimentation rate when P1 was compared with P3; iii) red blood cell count, hematocrit, and hemolysis index when P2 was compared with P3. Surprisingly, clinically significant differences were found only for sodium when P1 was compared with P2, and P1 was compared with P3. No fibrin filaments or microclots were observed in any samples.

Conclusion: Primary blood tubes mixing after collection with evacuated tube system appears to be unnecessary.