Solution Densities and Estimated Total Protein Contents Associated With Inappropriate Flotation of Separator Gel in Different Blood Collection Tubes

Context.—Clinical samples that have densities greater than that of separator gel in specimen tubes may exhibit gel flotation to the top of the specimen upon centrifugation. Inappropriate separator gel flotation can occur in specimens with high protein content. In automated analytical systems, gel flotation can lead to mechanical disruption and potential inaccurate result reporting upon aspiration into instrument sampling probes. Objective.—To determine the relative specimen densities and estimated total protein contents at which specimen gel flotation would occur upon centrifugation in commonly used commercial specimen tubes, a comparative study of separator gel density was initiated using prepared dextran solutions. Design.—Specific gravity of several dextran solutions was determined by direct hydrometry. The dextran solutions were introduced to serum and plasma lithium heparin BD Vacutainer specimen tubes manufactured by Becton, Dickinson and Company and into Vacuette specimen tubes manufactured by Greiner Bio-One containing separator gel. Following centrifugation the specimen tubes were examined for gel flotation. Results.—Flotation was observed at a lower dextran solution density for Greiner than for BD tubes in both serum and plasma separator gel specimen tubes. Additionally, some differences between specimen tube lots were observed for both BD and Greiner tubes. The total protein content in clinical samples that would result in gel flotation can be estimated for different specimen container types. Conclusions.—Differences were observed for the gel separator specific gravity in different blood collection containers. Laboratories wishing to avoid problems with inappropriate gel flotation in high protein samples should consider these observations.